Polymer gel electrolyte, secondary cell, and electrical double-layer capacitor

ABSTRACT

A polymer gel electrolyte includes an electrolyte solution composed of a plasticizer with at least two carbonate structures on the molecule and an electrolyte salt, in combination with a matrix polymer. Secondary batteries made with the polymer gel electrolyte can operate at a high capacitance and a high current, have a broad service temperature range and a high level of safety, and are thus particularly well-suited for use in such applications as lithium secondary cells and lithium ion secondary cells. Electrical double-layer capacitors made with the polymer gel electrolyte have a high output voltage, a large output current, a broad service temperature range and excellent safety.

BACKGROUND OF THE INVENTION

[0001] 1. Field of the Invention

[0002] The present invention relates to novel polymer gel electrolytesprepared by solidifying a high-boiling fire-retarding plasticizer, andto secondary cells and electrical double-layer capacitors made usingsuch polymer gel electrolytes.

[0003] 2. Prior Art

[0004] Non-aqueous electrolyte solution-based secondary cells such aslithium secondary cells have attracted much attention in recent years onaccount of their high voltage and high energy density. The solvent usedin such non-aqueous electrolyte solutions is a mixed solvent composed ofa cyclic carbonate or lactone having a high dielectric constant and ahigh viscosity, such as propylene carbonate (PC), ethylene carbonate(EC) or y-butyrolactone (GBL), in combination with a low-viscosityacyclic carbonate, such as dimethyl carbonate (DMC) or diethyl carbonate(DEC), or a low-viscosity ether such as 1, 2-dimethoxyethane (DME),diglyme or dioxolane.

[0005] Further improvements in safety, such as fire retardance andnon-flammability, will be needed to attain even higher levels of energydensity and output density. Yet, such goals have been very difficult toachieve with existing low-flash-point flammable non-aqueous electrolytesolutions.

[0006] A number of solutions have already been proposed, includingmethods involving the addition of a flame-retarding phosphate to theelectrolyte solution (JP-A 4-184870 and JP-A 8-88023) and methodsinvolving the addition of an alkylene carbonate or a halogenatedalkylene carbonate to the electrolyte solution (JP-A 9-306542), JP-A9-312171, JP-A 10-251401, JP-A 12-260467). However, in batteries andelectrical double-layer capacitors made with such electrolytes, thesupporting electrolyte salt has a poor solubility, resulting in a lowionic conductivity. In addition, undesirable effects such as fluidleakage to the exterior and leaching out of the electrode material tendto arise, compromising the long-term reliability of the battery orcapacitor.

[0007] By contrast, batteries and electrical double-layer capacitorsmade with solid electrolytes are free of such problems and offer theadditional advantage of being easy to form into a thin shape.

[0008] U.S. Pat. No. 4,792,504 describes a method for improving ionicconductivity by using a polymer gel electrolyte prepared by impregnatingpolyethylene oxide with an electrolyte solution composed of a metal saltand an aprotic solvent, but this polymer gel electrolyte does not have asufficient ionic conductivity or film strength. To overcome thisproblem, JP-A 6-187822 discloses an ion-conductive solid polymerelectrolyte made with a complex composed of an electrolyte and a polymerthat is prepared from a mixture of oxyalkylene group-bearing(meth)acrylate monomers having urethane linkages.

[0009] However, a system prepared by gelating a non-aqueous electrolytewhich is flammable and has a relatively low flash point is subject tothe same service temperature range limitations due to solventvaporization and gelation as solutions of the non-aqueous electrolyte.In addition, there are problems with polymer gel electrolyte productionand with the safety of batteries and electrical double-layer capacitorsin which such electrolytes are used.

SUMMARY OF THE INVENTION

[0010] It is therefore a first object of the invention to provide anovel polymer gel electrolyte which is endowed with a fire retardance, aservice temperature range and stable voltage range that are both broad,and a high ionic conductivity at ambient and low temperatures withoutcompromising such characteristics of devices in which it is used ascharge/discharge efficiency, energy density, output density and servicelife.

[0011] A second object of the invention is to provide a secondary cellwhich can be operated at a high capacity and high current, which has abroad service temperature range, and which has excellent safety by usingthe foregoing polymer gel electrolyte of the invention.

[0012] A third object of the invention is to provide an electricaldouble-layer capacitor which has a high output voltage, a large outputcurrent, a broad service temperature range and excellent safety by usingthe foregoing polymer gel electrolyte of the invention.

[0013] We have found that by using as the electrolyte for secondarycells and electrical double-layer capacitors a polymer gel electrolytecomposed of a matrix polymer and an electrolyte solution containing botha plasticizer with at least two carbonate structures on the molecule andan electrolyte salt, it is possible to obtain high-performance secondarycells and electrical double-layer capacitors which have fire retardance,a high ionic conductivity at ambient and low temperatures, and a servicetemperature range and stable voltage range which are both broad withoutany loss in such device characteristics as the charge/dischargeefficiency, energy density, output density and service life.

[0014] Accordingly, in a first aspect, the invention provides a polymergel electrolyte which is composed of an electrolyte solution containinga plasticizer with at least two carbonate structures on the molecule andan electrolyte salt, and is also composed of a matrix polymer.

[0015] Preferably, the polymer gel electrolyte consists essentially ofthe plasticizer with at least two carbonate structures on the molecule,the electrolyte salt, and the matrix polymer.

[0016] In the above-described polymer gel electrolyte, the plasticizerwith at least two carbonate structures on the molecule is preferably acompound of general formula (1) below

[0017] wherein R¹ and R² are each independently a substituted orunsubstituted monovalent hydrocarbon group of 1 to 10 carbons, and R³and R⁴ are each independently a substituted or unsubstituted divalenthydrocarbon group of 1 to 20 carbons, with the proviso that any two ofthe moieties R¹, R², R³ and R⁴ may together form a ring; X is —OCO—,—COO—, —COO—, —CONR⁵—, —NR⁶CO— (R⁵ and R⁶ being hydrogen or an alkyl of1 to 4 carbons), —0— or an arylene group; and the letters m, n, k and pare each independently 0 or an integer from 1 to 10. Some or all of thehydrogen atoms on the plasticizer of general formula (1) having at leasttwo carbonate structures on the molecule are typically substituted withhalogen atoms.

[0018] In one preferred embodiment of the polymer gel electrolyteaccording to the first aspect of the invention, the matrix polymer inthe polymer gel electrolyte is an unsaturated polyurethane compoundprepared by reacting:

[0019] (A) an unsaturated alcohol having at least one (meth)acryloylgroup and a hydroxyl group on the molecule;

[0020] (B) a polyol compound of general formula (2) below

HO—[(R⁷)_(h)—(Y)_(i)—(R⁸)_(j)]—OH  (2)

[0021] wherein R⁷ and R⁸ are each independently a divalent hydrocarbongroup of 1 to 10 carbons which may contain an amino, nitro, carbonyl orether group,

[0022] Y is —OCOO—, —COO—, —NR⁹CO— (R⁹ being hydrogen or an alkyl groupof 1 to 4 carbons), —O— or an arylene group, the letters h, i and j areeach independently 0 or an integer from 1 to 10, and the letter q is anumber which is ≧1;

[0023] (C) a polyisocyanate compound; and

[0024] (D) an optional chain extender.

[0025] In another preferred embodiment of the polymer gel electrolyteaccording to the invention, the matrix polymer is a polymeric materialhaving an interpenetrating network structure or a semi-interpenetratingnetwork structure, and especially one composed of a hydroxyalkylpolysaccharide derivative, a polyvinyl alcohol derivative or apolyglycidol derivative in combination with a crosslinkable functionalgroup-bearing compound, part or all of which compound is the unsaturatedpolyurethane compound described above.

[0026] In yet another preferred embodiment, the matrix polymer is athermoplastic resin containing units of general formula (3) below

[0027] wherein the letter r is an integer from 3 to 5, and the letter sis an integer ≧5.

[0028] In still another preferred embodiment, the matrix polymer is afluoropolymer material.

[0029] The electrolyte salt in any of the above polymer gel electrolytesis preferably at least one selected from the group consisting of alkalimetal salts, quaternary ammonium salts, quaternary phosphonium salts andtransition metal salts.

[0030] In a second aspect, the invention provides a secondary cellhaving a positive electrode, a negative electrode and an electrolyte,which electrolyte is a polymer gel electrolyte according to theabove-described first aspect of the invention. The negative electrodepreferably includes a negative electrode active material which islithium, a lithium alloy or a carbon material capable of adsorbing andreleasing lithium ions. The positive electrode preferably includes apositive electrode active material which is an electrically conductivepolymer, a metal oxide, a metal sulfide or a carbonaceous material.

[0031] In a third aspect, the invention provides an electricaldouble-layer capacitor composed of a pair of polarizable electrodes andan electrolyte between the polarizable electrodes, which electrolyte isa polymer gel electrolyte according to the above-described first aspectof the invention. Preferably, the polarizable electrodes containactivated carbon which is prepared by subjecting a mesophase pitch-basedcarbon material, a polyacrylonitrile-based carbon material, a gasphase-grown carbon material, a rayon-based carbon material or apitch-based carbon material to alkali activation with an alkali metalcompound, then grinding the activated carbon material.

[0032] The polymer gel electrolyte of the invention is composed of anelectrolyte solution containing a plasticizer having at least twocarbonate structures on the molecule and an electrolyte salt, incombination with a matrix polymer which pseudo-solidifies theelectrolyte solution. The plasticizer with at least two carbonatestructures on the molecule has the desirable attributes of a low vaporpressure, excellent fire retardance and a high safety. At the same time,it also has drawbacks, including the poor solubility of the supportingelectrolyte salt and a low ionic conductivity. We have discovered that amatrix polymer capable of dissolving and holding the supportingelectrolyte salt within the polymer chains, when used in combinationwith the plasticizer, forms a polymer gel electrolyte endowed not onlywith a low vapor pressure, excellent fire retardance and high safety,but also with a very large degree of ion dissociation and excellentionic conductivity under both ambient and low temperatures.

[0033] In the combination of a plasticizer with a matrix polymer thatmakes up the polymer gel electrolyte of the invention, the componentmaterials have a high mutual affinity, preventing undesirable effectssuch as liquid exudation from the gel and re-dissolution. Hence, the gelhas a good physical stability and is well-suited for use as theelectrolyte in secondary batteries such as lithium secondary cells andlithium ion secondary cells, and in electrical double-layer capacitors.

[0034] The combination of a plasticizer and a matrix polymer making upthe polymer gel electrolyte of the invention can be employed as all ofthe polymeric material used between both current collectors in asecondary battery or an electrical double-layer capacitor. That is, itis not limited only to use as an electrolyte film, but is also highlysuitable for use as an ion-conductive separator and as a binder polymerin electrode compositions.

[0035] Secondary batteries made using the polymer gel electrolyte of theinvention can be operated at a high capacity and high current, have abroad service temperature range, and have excellent safety. Moreover,electrical double-layer capacitors made using the inventive polymer gelelectrolyte are high-performance devices having a high output voltage, alarge output current, a broad service temperature range and excellentsafety.

BRIEF DESCRIPTION OF THE DIAGRAM

[0036]FIG. 1 is a sectional view of a laminate-type secondary cell orelectrical double-layer capacitor according to one embodiment of theinvention.

DETAILED DESCRIPTION OF THE INVENTION

[0037] The objects, features and advantages of the invention will becomemore apparent from the following detailed description, taken inconjunction with the foregoing diagram.

Polymer Gel Electrolyte of the Invention

[0038] The polymer gel electrolyte of the invention is composed of anelectrolyte solution containing a plasticizer with at least twocarbonate structures on the molecule and an electrolyte salt, incombination with a matrix polymer. The use in particular of a polymergel electrolyte which consists essentially of a plasticizer with atleast two carbonate structures on the molecule, an electrolyte salt anda matrix polymer, and which does not contain another non-aqueouselectrolyte solution, is preferable for preventing the evolution of gaswithin the battery or capacitor housing and for enhancing safety.

[0039] The plasticizer with at least two carbonate structures on themolecule may be any plasticizer of this type which is liquid within theservice temperature range of the secondary battery or electricaldouble-layer capacitor, although one having a low liquid viscosity and alow vapor pressure is preferred. Plasticizers with a high liquidviscosity are industrially difficult to handle and have a low ionicconductivity. Plasticizers with a high vapor pressure may lead to theevolution of gas within the device housing during use in a secondarybattery or an electrical double-layer capacitor, giving rise to safetyconcerns. Specifically, a plasticizer of the above type which is liquidwithin a service temperature range of −30 to +120° C., and especially−20 to +100° C., which has a liquid viscosity within this servicetemperature range of not more than 10 mPa·s, and especially not morethan 5 mPa·s, and which has a vapor pressure at 25° C. of not more than10 mbar, and especially 0 to 10 mbar, is preferred.

[0040] The plasticizer with at least two carbonate structures on themolecule is most preferably a compound of general formula (1) below

[0041] In the formula, R¹ and R² are each independently a substituted orunsubstituted monovalent hydrocarbon group of 1 to 10, and preferably 1to 8 carbons. Illustrative examples include alkyls such as methyl,ethyl, propyl, isopropyl, butyl, isobutyl, tert-butyl, pentyl,neopentyl, hexyl, cyclohexyl, octyl, nonyl and decyl; aryls such asphenyl, tolyl and xylyl; aralkyls such as benzyl, phenylethyl andphenylpropyl; alkenyls such as vinyl, allyl, propenyl, isopropenyl,butenyl, hexenyl, cyclohexyl and octenyl; and any of the foregoinggroups in which some or all of the hydrogen atoms have been substitutedwith a halogen (e.g., fluorine, bromine, chlorine), cyano, hydroxyl,H(OR¹⁰)_(z)— (wherein R¹⁰ is an alkylene of 2 to 5 carbons, and theletter z is an integer from 1 to 100), amino, aminoalkyl or phosphono,such as cyanobenzyl, cyanoethyl and other cyanated alkyls, chloromethyl,chloropropyl, bromoethyl and trifluoropropyl. Any one or combination oftwo or more of the above groups may be used, although those groups inwhich some or all of the hydrogen atoms on R¹ and R² are substitutedwith halogen atoms (e.g., fluorine, chlorine, bromine) are preferredbecause the fire retardance can thus be further enhanced.

[0042] In above formula (1), R³ and R⁴ are each independently asubstituted or unsubstituted divalent hydrocarbon group of 1 to 20carbons, preferably a C₁₋₈ linear alkylene group, a C₆₋₁₈ alicyclicgroup-bearing alkylene group or a C₆₋₁₈ aromatic group-bearing alkylenegroup. The divalent hydrocarbon groups may have an intervening oxygenatom, sulfur atom, carbonyl group, carbonyloxy group,nitrogen-containing group such as NH, N(CH₃) or N(C₂H₅), or SO₂ group.Illustrative examples include alkylenes such as methylene, ethylene,trimethylene and propylene; arylenes such as phenylene, tolylene andxylylene; and aralkylenes such as benzylene, phenylethylene andphenylpropylene. Of the foregoing groups, those in which some or all ofthe hydrogen atoms on these groups are substituted with halogen atoms(e.g., fluorine, bromine, chlorine) are preferred because of theadditional enhancement in fire retardance.

[0043] Any two of the above moieties R¹, R², R³ and R⁴ may together forma ring.

[0044] In formula (1), X is —CO—, —COO—, —OCOO—, —CONR⁵—, NR⁶CO— (R⁵ andR⁶ being independently a hydrogen atom or an alkyl of 1 to 4 carbons),—O— or an arylene group such as phenylene. The letters m, n, k and p areeach independently 0 or an integer from 1 to 10.

[0045] Examples of such plasticizers having at least two carbonatestructures on the molecule includes compounds of the specific formulasshown below. These compounds may be used alone or as combinations of twoor more thereof.

[0046] CH₃-OCO₂-CH₂CH₂-OCO₂-CH₃,

[0047] CF₃-OCO2-CH₂CH₂ - OC0 ₂- CF₃,

[0048] CF₃-OCO₂-CF₂CF₂-OCO₂-CF₃,

[0049] C₂H₅-OCO₂-CH₂CH₂-OCO₂-C₂H₅,

[0050] C₂F₅-OCO₂-CH₂CH₂-OCO₂-C₂F₅,

[0051] C₂F₅-OCO₂-CF₂CF₂-OCO₂-C₂F₅,

[0052] C₃H₇-OCO₂-CH₂CH₂-OCO₂-C₃H₇,

[0053] C₃F₇-OCO₂-CH₂CH₂-OCO₂-C₃F₇,

[0054] C₃F₇-OCO₂-CF₂CF₂-OCO₂-C₃F₇,

[0055] C₄H₉-OCO₂-CH₂CH₂-OCO₂-C₄H₉,

[0056] C₄F₉-OCO₂-CH₂CH₂-OCO₂-C₄F₉,

[0057] C₄F₉-OCO₂-CF₂CF₂-OCO₂-C₄F₉,

[0058] C₆H₅-OCO₂-CH₂CH₂-OCO₂-C₆H₅,

[0059] C₆F₅-OCO₂-CH₂CH₂-OCO₂-C₆F₅,

[0060] C₆F₅-OCO₂-CF₂CF₂-OCO₂-C₆F₅,

[0061] C₆H₅CH₂-OCO₂-CH₂CH₂-OCO₂-CH₂C₆H₅,

[0062] C₆F₅CF₂-OCO₂-CH₂CH₂-OCO₂-CF₂C₆F₅,

[0063] C₆F₅CF₂-OCO₂-CF₂CF₂-OCO₂-CF₂C₆F₅,

[0064] CH₃-OCO₂-CH₂CH₂CH₂-OCO₂-CH₃,

[0065] CF₃-OCO₂-CH₂CH₂CH₂-OCO₂-CF₃,

[0066] CF₃-OCO₂-CF₂CF₂CF₂-OCO₂-CF₃,

[0067] C₂H₅-OCO₂-CH₂CH₂CH₂-OCO₂-C₂H₅,

[0068] C₂F₅-OCO₂-CH₂CH₂CH₂-OCO₂-C₂F₅,

[0069] C₂F₅-OCO₂-CF₂CF₂CF₂-OCO₂-C₂F₅,

[0070] C₃H₇-OCO₂-CH₂CH₂CH₂-OCO₂-C₃H₇,

[0071] C₃F₇-OCO₂-CH₂CH₂CH₂-OCO₂-C₃F₇,

[0072] C₃F₇-OCO₂-CF₂CF₂CF₂-OCO₂-C₃F₇,

[0073] C₄H₉-OC0 ₂-CH₂CH₂CH₂-OCO₂-C₄H₉,

[0074] C₄F₉-OCO₂-CH₂CH₂CH₂-OCO₂-C₄F₉,

[0075] C₄F₉-OCO₂-CF₂CF₂CF₂-OCO₂-C₄F₉,

[0076] C₆H₅-OCO₂-CH₂CH₂CH₂-OCO₂-C₆H₅,

[0077] C₆F₅-OCO₂-CH₂CH₂CH₂-OCO₂-C₆F₅,

[0078] C₆F₅-OCO₂-CF₂CF₂CF₂-OCO₂-C₆F₅,

[0079] C₆H₅CH₂-OCO₂-CH₂CH₂CH₂-OCO₂-CH₂C₆H₅,

[0080] C₆F₅CF₂-OCO₂-CH₂CH₂CH₂-OCO₂-CF₂C₆F₅,

[0081] C₆F₅CF₂-OCO₂-CF₂CF₂CF₂-OCO₂-CF₂C₆F₅,

[0082] CH₃-OCO₂-CH₂CH₂OCH₂CH₂-OCO₂-CH₃,

[0083] CF₃-OCO₂-CH₂CH₂OCH₂CH₂-OCO₂-CF₃,

[0084] CF₃-OCO₂-CF₂CF₂OCF₂CF₂-OCO₂-CF₃,

[0085] C₂H₅-OCO₂-CH₂CH₂OCH₂CH₂-OCO₂-C₂H₅,

[0086] C₂F₅-OCO₂-CH₂CH₂OCH₂CH₂-OCO₂-C₂F₅,

[0087] C₂F₅-OCO₂-CF₂CF₂OCF₂CF₂-OCO₂-C₂F₅,

[0088] C₃H₇-OCO₂-CH₂CH₂OCH₂CH₂-OCO₂-C₃H₇,

[0089] C₃F₇-OCO₂-CH₂CH₂OCH₂CH₂-OCO₂-C₃F₇,

[0090] C₃F₇-OCO₂-CF₂CF₂OCF₂CF₂-OCO₂-C₃F₇,

[0091] C₄H₉-OCO₂-CH₂CH₂OCH₂CH₂-OCO₂-C₄H₅,

[0092] C₄F -OCO₂-CH₂CH_(2 OCH) ₂CH₂-OCO₂-C₄F₉,

[0093] C₄F₉-OCO₂-CF₂CF₂OCF₂CF₂-OCO₂-C₄F₅,

[0094] C₆H₅-OCO₂-CH₂CH₂OCH₂CH₂-OCO₂-C₆H₅,

[0095] C₆F₅-OCO₂-CH₂CH₂OCH₂CH₂-OCO₂-C₆F₅,

[0096] C₆F₅-OCO₂-CF₂CF₂OCF₂CF₂-OCO₂-C₆F₅,

[0097] C₆H₅CH₂-OCO₂-CH₂OCH₂CH₂CH₂-OCO₂-CH₂C₆H₅,

[0098] C₆F₅CF₂-OCO₂-CH₂OCH₂CH₂CH₂-OCO₂-CF₂C₆F₅,

[0099] C₆F₅CF₂-OCO₂-CF₂OCF₂CF₂CF₂-OCO₂-CF₂C₆F₅,

[0100] The electrolyte salt serving as a constituent of the electrolytesolution in the invention may be any electrolyte salt, including alkalimetal salts and quaternary ammonium salts, that is used in devices suchas lithium secondary cells, lithium ion secondary cells and electricaldouble-layer capacitors. Suitable alkali metal salts include lithiumsalts, sodium salts and potassium salts, and more specifically:

[0101] (1) lithium salts such as lithium tetrafluoroborate, lithiumhexafluorophosphate, lithium perchlorate, lithiumtrifluoromethanesulfonate, the sulfonyl imide lithium salts of generalformula (4) below

(R¹¹—SO₂)(R¹²-SO₂)NLi  (4),

[0102] the sulfonyl methide lithium salts of general formula (5) below

(R¹³—SO₂)(R¹⁴—SO₂)(R¹⁵—SO₂)CLi  (5),

[0103] lithium acetate, lithium trifluoroacetate, lithium benzoate,lithium p-toluenesulfonate, lithium nitrate, lithium bromide, lithiumiodide and lithium tetraphenylborate;

[0104] (2) sodium salts such as sodium perchlorate, sodium iodide,sodium tetrafluoroborate, sodium hexafluorophosphate, sodiumtrifluoromethanesulfonate and sodium bromide;

[0105] (3) potassium salts such as potassium iodide, potassiumtetrafluoroborate, potassium hexafluorophosphate and potassiumtrifluoromethanesulfonate.

[0106] In above formulas (4) and (5), R¹¹ to R¹⁵ are each independentlyC₁₋₄ perfluoroalkyl groups which may have one or two ether linkages.

[0107] Illustrative examples of the sulfonyl imide lithium salts ofgeneral formula (4) include (CF₃SO₂)₂NLi, (C₂F₅SO₂)₂NLi, (C₃F₇SO₂)₂NLi,(C₄F₉SO₂)₂NLi, (CF₃SO₂)(C₂F₅SO₂)NLi, (CF₃SO₂)(C₃F₇SO₂)NLi, (CF₃SO₂)(C₄F₉SO₂)NLi, (C₂F₅SO₂)(C₃F₇SO₂)NLi, (c₂F₅SO₂)(C₄F₉SO₂)NLi and(CF₃OCF₂SO₂)₂NLi.

[0108] Illustrative examples of the sulfonyl methide lithium salts ofgeneral formula (5) include (CF₃SO₂)₃CLi, (C₂F₅SO₂)₃CLi, (C₃F₇SO₂)₃CLi,(C₄F₉SO₂)₃CLi, (CF₃SO₂)₂(C₂F₅SO₂)CLi, (CF₃SO₂)₂(C₃F₇SO₂)CLi,(CF₃SO₂)₂(C₄F₉SO₂)CLi, (CF₃SO₂) (C₂F₅SO₂)₂CLi, (CF₃SO₂)(C₃F₇SO₂)₂CLi,(CF₃SO₂) (C₄F₉SO₂)₂CLi, (C₂F₅SO₂)₂ (C₃F₇SO₂)CLi, (C₂F₅SO₂)₂(C₄F₉SO₂)CLiand (CF₃OCF₂SO₂)₃CLi.

[0109] Suitable quaternary ammonium salts include tetramethylammoniumhexafluorophosphate, tetraethylammonium hexafluorophosphate,tetrapropylammonium hexafluorophosphate, methyltriethylammoniumhexafluorophosphate, tetraethylammonium tetrafluoroborate andtetraethylammonium perchlorate; and also acylic amidines, cyclicamidines (e.g., imidazoles, imidazolines, pyrimidines,1,5-diazabicyclo[4.3.0]non-5-ene (DBN),1,8-diazabicyclo[5.4.0]undec-7-ene (DBU)), pyrroles, pyrazoles,oxazoles, thiazoles, oxadiazoles, thiadiazoles, triazoles, pyridines,pyrazines, triazines, pyrrolidines, morpholines, piperidines andpiperazines.

[0110] Of the above electrolyte salts, lithium tetrafluoroborate,lithium hexafluorophosphate, sulfonyl imide lithium salts of generalformula (4) and sulfonyl methide lithium salts of general formula (5)are preferred because of their particularly high ionic conductivity andexcellent thermal stability. These electrolyte salts may be used singlyor as combinations of two or more thereof.

[0111] Aside from the above-mentioned electrolyte salts, polymer gelelectrolytes to be used in electrical double-layer capacitors mayinclude other electrolyte salts commonly employed in electricaldouble-layer capacitors. Preferred examples include salts obtained bycombining a quaternary onium cation of the general formulaR¹¹R¹²R¹³R¹⁴N⁺ or R¹¹R¹²R¹³R¹⁴P+ (wherein R¹¹ to R¹⁴ are eachindependently alkyls of 1 to 10 carbons) with an anion such as BF₄ ⁻,N(CF₃SO₂)₂ ⁻, PF₆ ⁻ or ClO₄ ⁻.

[0112] Illustrative examples include (C₂H₅)₄PBF₄, (C₃H₇)₄PBF₄,(C₄H₉)₄PBF₄, (C₆H₁₃)₄PBF₄, (C₄H₉)₃CH₃PBF₄, (C₂H₅)₃(Ph-CH₂)PBF₄ (whereinPh stands for phenyl), (C₂H₅)₄PPF₆, (C₂H₅)PCF₃SO₂, (C₂H₅)₄NBF₄,(C₄H₉)₄NBF₄, (C₆H₁₃)₄NBF₄, (C₂H₅)₆NPF₆, LiBF₄ and LiCF₃SO₃. These may beused alone or as combinations of two or more thereof.

[0113] The concentration of the electrolyte salt in the electrolytesolution is generally 0.05 to 3 mol/L, and preferably 0.1 to 2 mol/L.Too low a concentration may make it impossible to obtain a sufficientionic conductivity, whereas too high a concentration may preventcomplete dissolution in the solvent.

[0114] In addition to the above-described plasticizer having at leasttwo carbonate structures on the molecule and the above-describedelectrolyte salt, the electrolyte solution in the invention may includealso a commonly used non-aqueous electrolyte solution insofar as theobjects of the invention are not compromised. Examples of suchnon-aqueous electrolyte solutions include cyclic and acyclic carbonates,acyclic carboxylates, cyclic and acyclic ethers, phosphates, lactonecompounds, nitrile compounds and amide compounds, as well as mixturesthereof.

[0115] Examples of suitable cyclic carbonates include alkylenecarbonates such as propylene carbonate (PC), ethylene carbonate (EC) andbutylene carbonate. Examples of suitable acyclic carbonates includedialkyl carbonates such as dimethyl carbonate (DMC), methyl ethylcarbonate (MEC) and diethyl carbonate (DEC). Examples of suitableacyclic carboxylates include methyl acetate and methyl propionate.Examples of suitable cyclic or acyclic ethers include tetrahydrofuran,1,3-dioxolane and 1,2-dimethoxyethane. Examples of suitable phosphatesinclude trimethyl phosphate, triethyl phosphate, ethyldimethylphosphate, diethylmethyl phosphate, tripropyl phosphate, tributylphosphate, tri(trifluoromethyl) phosphate, tri(trichloromethyl)phosphate, tri(trifluoroethyl) phosphate, tri(perfluoroethyl) phosphate,2-ethoxy-1,3,2-dioxaphosphoran-2-one,2-trifluoroethoxy-1,3,2-dioxaphosphoran-2-one and2-methoxyethoxy-1,3,2-dioxaphosphoran-2-one. An example of a suitablelactone compound is γ-butyrolactone. An example of a suitable nitrilecompound is acetonitrile. An example of a suitable amide compound isdimethylformamide. Of these, cyclic carbonates, acyclic carbonates,phosphates and mixtures thereof are preferred because they elicit adesirable battery performance such as high charge/dischargecharacteristics and high output characteristics.

[0116] The plasticizer having at least two carbonate structures on themolecule accounts for preferably 10 to 99 wt % of the overallelectrolyte solution. For reasons having to do with battery performance(e.g., charge/discharge characteristics), a plasticizer content of 30 to99 wt % is especially preferred. Too little plasticizer may fail toconfer sufficient fire retardance, whereas too much may lower the amountof electrolyte solution for carrying out gelation to such a degree as tomake it impossible to achieve a sufficient shape retention andsufficient physical strength in the polymer gel electrolyte.

[0117] If necessary, any one or more of various types of compounds, suchas polyimides, polyacetanols, polyalkylene sulfides, polyalkyleneoxides, cellulose esters, polyvinyl alcohols, polybenzoimidazoles,polybenzothiazoles, silicone glycols, vinyl acetate, acrylic acid,methacrylic acid, polyether-modified siloxanes, polyethylene oxides,amide compounds, amine compounds, phosphoric acid compounds andfluorinated nonionic surfactants, may also be included in theelectrolyte solution of the invention for such reasons as to lower theresistance at the interface between the positive and negative electrodesand thereby improve the charge/discharge cycle characteristics or toenhance the wettability with the separator. Of these compounds,fluorinated nonionic surfactants are especially preferred.

[0118] The matrix polymer in the polymer gel electrolyte of theinvention is preferably one which has a high affinity with theplasticizer and which, even after gelation, does not give rise to liquidexudation and re-dissolution. Examples of such polymers include (I)unsaturated polyurethane compounds, (II) polymeric materials having aninterpenetrating network structure or a semi-interpenetrating networkstructure, (III) thermoplastic resins containing units of above generalformula (3), and (IV) fluoropolymer materials.

[0119] The use of one of polymeric materials (I) to (III) as the matrixpolymer results in a high adhesion, and can therefore increase thephysical strength of the polymer gel electrolyte. Polymeric materialshaving an interpenetrating network structure or a semi-interpenetratingnetwork structure (II) are characterized by a high affinity between theelectrolyte solvent molecules and the ionic molecules, a high ionmobility, the ability to dissolve the electrolyte salt to a highconcentration, and a high ionic conductivity. Thermoplastic resins (III)which contain units of general formula (3) are thermoplastic and thuscan be easily shaped, suitably absorb organic electrolyte solutions andswell, and have a high ionic conductivity. Fluoropolymer materials (IV)have excellent thermal and electrical stability.

[0120] The above-described unsaturated polyurethane compounds (I) arepreferably ones prepared by reacting:

[0121] (A) an unsaturated alcohol having at least one (meth)acryloylgroup and a hydroxyl group on the molecule;

[0122] (B) a polyol compound of general formula (2) below

HO—[(R⁷)_(h)—(Y)_(i)—(R⁸)_(j)]_(q)—OH  (2)

[0123] wherein R⁷ and R⁸ are each independently a divalent hydrocarbongroup of 1 to 10 carbons which may contain an amino, nitro, carbonyl orether group,

[0124] Y is —COO—, —OCOO—, —NR⁹CO— (R⁹ being a hydrogen atom or an alkylgroup of 1 to 4 carbons), —O— or an arylene group,

[0125] the letters h, i and j are each independently 0 or an integerfrom 1 to 10, and

[0126] the letter q is a number which is ≧1;

[0127] (C) a polyisocyanate compound; and

[0128] (D) an optional chain extender.

[0129] The unsaturated alcohol serving as component (A) is not subjectto any particular limitation, provided the molecule bears at least one(meth)acryloyl group and a hydroxyl group. Illustrative examples include2-hydroxyethyl acrylate, 2-hydroxypropyl acrylate, 2-hydroxyethylmethacrylate, 2-hydroxylpropyl methacrylate, diethylene glycolmonoacrylate, diethylene glycol monomethacrylate, triethylene glycolmonoacrylate and triethylene glycol monomethacrylate.

[0130] The polyol compound serving as component (B) may be, for example,a polyether polyol such as polyethylene glycol, polypropylene glycol,polyoxytetramethylene glycol, ethylene glycol-propylene glycol copolymeror ethylene glycol-oxytetramethylene glycol copolymer; or a polyesterpolyol such as polycaprolactone. A polyol compound of general formula(2) below is especially preferred:

HO—[(R⁷)_(h)—(Y)_(i)—(R⁸)_(j)]_(q)—OH  (2).

[0131] In the foregoing formula, R⁷ and R⁸ are each independently adivalent hydrocarbon group of 1 to 10 carbons, and preferably 1 to 6carbons, which may contain an amino, nitro, carbonyl or ether group.Alkylene groups such as methylene, ethylene, trimethylene, propylene,ethylene oxide and propylene oxide are especially preferred. Y is —COO—,—OCOO—, —NR⁹CO— (R⁹ being a hydrogen atom or an alkyl group of 1 to 4carbons), —O— or an arylene group such as phenylene. The letters h, iand j are each independently 0 or an integer from 1 to 10. The letter qis a number which is ≧1, preferably ≧5, and most preferably from 10 to200.

[0132] The polyol compound serving as component (B) has a number-averagemolecular weight of preferably 400 to 10,000, and more preferably 1,000to 5,000.

[0133] Illustrative examples of the polyisocyanate compound serving ascomponent (C) include aromatic diisocyanates such as tolylenediisocyanate, 4,4′-diphenylmethane diisocyanate, p-phenylenediisocyanate, 1,5-naphthylene diisocyanate,3,3′-dichloro-4,4′-diphenylmethane diisocyanate and xylylenediisocyanate; and aliphatic or alicyclic diisocyanates such ashexamethylene diisocyanate, isophorone diisocyanate,4,4′-dichlorohexylmethane diisocyanate and hydrogenated xylylenediisocyanate.

[0134] The unsaturated polyurethane compound in the invention ispreferably one prepared from above components (A) to (C) and also, ifnecessary, a chain extender. Any chain extender commonly employed in thepreparation of thermoplastic polyurethane resins may be used.Illustrative examples include aliphatic diols such as ethylene glycol,diethylene glycol, propylene glycol, 1,3-propanediol, 1,4-butanediol,1,5-pentanediol, 1,6-hexanediol, 1,7-heptanediol, 1,8-octanediol and1,9-nonanediol; aromatic or alicyclic diols such as1,4-bis(β-hydroxyethoxy)benzene, 1,4-cyclohexanediol,bis(β-hydroxyethyl) terephthalate and xylylene glycol; diamines such ashydrazine, ethylenediamine, hexamethylenediamine, propylenediamine,xylylenediamine, isophoronediamine, piperazine, piperazine derivatives,phenylenediamine and tolylenediamine; and amino alcohols such as adipoylhydrazide and isophthaloyl hydrazide. Any one or combinations of two ormore of these may be used.

[0135] Use may also be made of a urethane prepolymer prepared by thepreliminary reaction of the polyol compound serving as component (B)with the polyisocyanate compound serving as component (C).

[0136] In preparing an unsaturated polyurethane compound for use in theinvention, it is advantageous to react components (A) to (D) in thefollowing proportions:

[0137] (A) 100 parts by weight of the unsaturated alcohol;

[0138] (B) 100 to 20,000 parts by weight, and preferably 1,000 to 10,000parts by weight, of the polyol compound;

[0139] (C) 80 to 5,000 parts by weight, and preferably 300 to 2,000parts by weight, of the polyisocyanate compound; and, optionally,

[0140] (D) 5 to 1,000 parts by weight, and preferably 10 to 500 parts byweight, of the chain extender.

[0141] Examples of unsaturated polyurethane compounds that can beprepared as described above include the following compounds. Any one orcombinations of two or more of these compounds may be used in thepresent invention.

[0142] (1)CH₂═C(CH₃)COO—C₂H₄O—CONH—C₆H₄—CH₂C₆H₄—NHCOO—[(C₂H₄O)_(h)—(CH₂CH(CH₃)O)_(j)]₉—CONH—C₆H₄—CH₂C₆H₄—NHCOO—C₂H₄O—COC(CH₃)═CH₂ (wherein h is 7, j is 3, and q is 5 to 7)

[0143] Component (A): hydroxyethyl methacrylate

[0144] Component (B): ethylene oxide/propylene oxide random copolymerdiol (in general formula (2) above, the ratio h/j is 7/3; thenumber-average molecular weight is about 3,000)

[0145] Component (C): 4,4′-diphenylmethane diisocyanate (2)CH₂—C(CH₃)COO—C₂H₄O—CONH—C₆H₄—CH₂C₆H₄—NHCOO—{[(C₂H₄O)_(h)(CH₂CH—(CH₃)O)_(j)]_(q)—CONH—C₆H₄—CH₂C₆H₄—NHCOO—C₄H₈O}_(r)—CONH—C₆H₄—CH₂C₆H₄—NHCOO—C₂H₄O—COC(CH₃)═CH₂

[0146] (wherein h is 7, j is 3, q is 5 to 7, and r is 2 to 20)

[0147] Component (A): hydroxyethyl methacrylate

[0148] Component (B): ethylene oxide/propylene oxide random copolymerdiol (in general formula (2) above, the ratio h/j is 7/3; thenumber-average molecular weight is about 3,000)

[0149] Component (C): 4,4′-diphenylmethane diisocyanate p1 Component(D): 1,4-butanediol (3)CH₂═C(CH₃)COO—C₂H₄O—CONH—C₆H₇(CH₃)₃—CH₂—NHCOO—[(C₂H₄O)_(h)(CH₂CH(CH₃)O)_(j)]_(q)—CONH—C₆H₇(CH₃)₃—CH₂—NHCOO—C₂H₄O—COC(CH₃)═CH₂

[0150] (wherein h is 7, j is 3, and q is 5 to 7)

[0151] Component (A): hydroxyethyl methacrylate

[0152] Component (B): ethylene oxide/propylene oxide random copolymerdiol (in general formula (2) above, the ratio h/j is 7/3; thenumber-average molecular weight is about 3,000)

[0153] Component (C): isophorone diisocyanate (4)CH₂═C(CH₃)COO—C₂H₄O—CONH—C₆H₄—CH₂C₆H₄—NHCOO—CH₂CH₂O—(COC₅H₁₀O)_(s)—CH₂CH₂O—CONH—C₆H₄—CH₄C₆H₄—NHCOO—C₂H₄O—COC(CH₃)═CH₂

[0154] (wherein s is 20 to 30)

[0155] Component (A): hydroxyethyl methacrylate

[0156] Component (B): polycaprolactone diol (number-average molecularweight, about 3,000)

[0157] Component (C): 4,4′-diphenylmethane diisocyanate

[0158] The resulting unsaturated polyurethane compound has anumber-average molecular weight of preferably 1,000 to 50,000, and mostpreferably 3,000 to 30,000. Too small a number-average molecular weightresults in the cured gel having a small molecular weight betweencrosslink sites, which may result in the polymer gel electrolyte havinginsufficient flexibility. On the other hand, a number-average molecularweight that is too large may cause the viscosity of the polymerelectrolyte solution before the gel cures to become so large as to makethe gel difficult to incorporate into a secondary battery or anelectrical double-layer capacitor.

[0159] In the practice of the invention, concomitant use may also bemade of a monomer which is copolymerizable with the unsaturatedpolyurethane compound. Examples of such monomers include acrylonitrile,methacrylonitrile, acrylic acid esters, methacrylic acid esters andN-vinylpyrrolidone. The concomitant use of acrylonitrile ormethacrylonitrile is advantageous for increasing the strength of thefilm without compromising the ionic conductivity. The monomer componentcopolymerizable with the unsaturated polyurethane compound is typicallyincluded in an amount, expressed in mole equivalents of unsaturateddouble bond groups per liter of the electrolyte solution prior to curingof the gel, of 0.5 to 5.0, and preferably 1.0 to 2.5. Too little monomercomponent may fail to produce a sufficient crosslinking reaction, andmay in turn fail to result in gelation. On the other hand, too muchmonomer component may lower the molecular weight between crosslink sitesso such as degree as to result in an excessive decline in theflexibility of the polymer gel electrolyte.

[0160] The unsaturated polyurethane compound (I) is typicallyincorporated in an amount of 0.5 to 30 wt %, and preferably 1 to 20 wt%, based on the overall polymer gel electrolyte.

[0161] The above-mentioned polymeric material having an interpenetratingnetwork structure or semi-interpenetrating network structure (II) may becomposed of two or more compounds, such as polymers or reactivemonomers, that are capable of forming a mutually interpenetrating orsemi-interpenetrating network structure.

[0162] Examples of the two or more compounds include:

[0163] (A) matrix polymers formed by combining (a) a hydroxyalkylpolysaccharide derivative with (d) a crosslinkable functionalgroup-bearing compound;

[0164] (B) matrix polymers formed by combining (b) a polyvinyl alcoholderivative with (d) a crosslinkable functional group-bearing compound;and

[0165] (C) matrix polymers formed by combining (c) a polyglycidolderivative with (d) a crosslinkable functional group-bearing compound.Use of the above-described unsaturated polyurethane compound (I) of theinvention as part or all of the crosslinkable functional group-bearingcompound (d) is advantageous for improving physical strength and otherreasons.

[0166] Any of the following may be used as the hydroxyalkylpolysaccharide derivative serving as component (a) of above matrixpolymer A:

[0167] (1) hydroxyethyl polysaccharides prepared by reacting ethyleneoxide with a naturally occurring polysaccharide such as cellulose orstarch,

[0168] (2) hydroxypropyl polysaccharides prepared by similarly reactinginstead propylene oxide,

[0169] (3) dihydroxypropyl polysaccharides prepared by similarlyreacting instead glycidol or 3-chloro-1,2-propanediol. Some or all ofthe hydroxyl groups on these hydroxyalkyl polysaccharides may be cappedwith an ester-bonded or ether-bonded substituent.

[0170] Illustrative examples of such polysaccharides include cellulose,starch, amylose, amylopectin, pullulan, curdlan, mannan, glucomannan,arabinan, chitin, chitosan, alginic acid, carrageenan and dextran. Thepolysaccharide is not subject to any particular limitations with regardto molecular weight, the presence or absence of a branched structure,the type and arrangement of constituent sugars in the polysaccharide andother characteristics. The use of cellulose and pullulan is especiallypreferred, in part because of their ready availability.

[0171] A method for synthesizing dihydroxypropyl cellulose is describedin U.S. Pat. No. 4,096,326. Other dihydroxypropyl polysaccharides can besynthesized by known methods, such as those described by Sato et al. inMakromol. Chem. 193, p. 647 (1992) or in Macromolecules 24, p. 4691(1991).

[0172] Hydroxyalkyl polysaccharides that may be used in the inventionhave a molar degree of substitution of preferably at least 2. At a molarsubstitution below 2, the ability to dissolve ion-conductive metal saltsbecomes so low as to make use of the hydroxyalkyl polysaccharideimpossible. The upper limit in the molar substitution is preferably 30,and more preferably 20. The industrial synthesis of hydroxyalkylpolysaccharides having a molar substitution greater than 30 can bedifficult on account of industrial production costs and the complexityof the synthesis operations. Moreover, even if one does go to the extratrouble of producing hydroxyalkyl polysaccharides having a molarsubstitution greater than 30, the increase in electrical conductivityresulting from the higher molar substitution is not likely to be verylarge.

[0173] The hydroxyalkyl polysaccharide derivative used as component (a)in the practice of the invention is one in which at least 10% of theterminal OH groups on the molecular chains of the above-describedhydroxyalkyl polysaccharide have been capped with one or more monovalentgroup selected from among halogen atoms, substituted or unsubstitutedmonovalent hydrocarbon groups, R¹⁵CO— groups (wherein R¹⁵ is asubstituted or unsubstituted monovalent hydrocarbon group), R¹⁵ ₃Si—groups (wherein R¹⁵ is the same as above), amino groups, alkylaminogroups, H(OR¹⁶)_(m)— groups (wherein R¹⁶ is an alkylene group of 2 to 5carbons, and the letter m is an integer from 1 to 100), andphosphorus-containing groups.

[0174] The above substituted or unsubstituted monovalent hydrocarbongroups are exemplified by the same groups as those mentioned above forR¹ and R², and preferably have 1 to 10 carbons.

[0175] The terminal OH groups may be capped using any known method forintroducing the respective groups.

[0176] The hydroxyalkyl polysaccharide derivative serving as component(a) is typically included in an amount of 0.5 to 30 wt %, and preferably1 to 20 wt %, based on the overall polymer gel electrolyte.

[0177] In the polyvinyl alcohol derivative serving as component (b) ofabove matrix polymer B, some or all of the hydroxyl groups on thepolymeric compound having oxyalkylene chain-bearing polyvinyl alcoholunits may be substituted. Here, “hydroxyl groups” refers collectively toremaining hydroxyl groups from the polyvinyl alcohol units and hydroxylgroups on the oxyalkylene-containing groups introduced onto themolecule.

[0178] The polymeric compound having polyvinyl alcohol units has anaverage degree of polymerization of at least 20, preferably at least 30,and most preferably at least 50. Some or all of the hydroxyl groups onthe polyvinyl alcohol units are substituted with oxyalkylene-containinggroups. The upper limit in the average degree of polymerization ispreferably no higher than 2,000, and most preferably no higher than 200.The average degree of polymerization refers herein to the number-averagedegree of polymerization. Polymeric compounds with too high a degree ofpolymerization have an excessively high viscosity, making them difficultto handle. Accordingly, the range in the degree of polymerization ispreferably from 20 to 500 monomeric units.

[0179] These polyvinyl alcohol units make up the mainchain of thepolyvinyl alcohol derivative and have the following general formula (6).

[0180] In formula (6), the letter n is at least 20, preferably at least30, and most preferably at least 50. The upper limit for n is preferablyno higher than 2,000, and most preferably no higher than 200.

[0181] It is highly advantageous for the polyvinyl alcoholunit-containing polymeric compound to be a homopolymer which satisfiesthe above range in the average degree of polymerization and in which thefraction of polyvinyl alcohol units within the molecule is at least 98mol %. However, use can also be made of, without particular limitation,polyvinyl alcohol unit-containing polymeric compounds which satisfy theabove range in the average degree of polymerization and have a polyvinylalcohol fraction of preferably at least 60 mol %, and more preferably atleast 70 mol %. Illustrative examples include polyvinylformal in whichsome of the hydroxyl groups on the polyvinyl alcohol have been convertedto formal, modified polyvinyl alcohols in which some of the hydroxylgroups on the polyvinyl alcohol have been alkylated, poly(ethylene vinylalcohol), partially saponified polyvinyl acetate, and other modifiedpolyvinyl alcohols.

[0182] Some or all of the hydroxyl groups on the polyvinyl alcohol unitsof the polymeric compound are substituted with oxyalkylene-containinggroups (moreover, some of the hydrogen atoms on these oxyalkylene groupsmay be substituted with hydroxyl groups) to an average molarsubstitution of at least 0.3. The proportion of hydroxyl groupssubstituted with oxyalkylene-containing groups is preferably at least 30mol %, and more preferably at least 50 mol %.

[0183] The average molar substitution (MS) can be determined byaccurately measuring the weight of the polyvinyl alcohol charged and theweight of the reaction product. Let us consider, for example, a case inwhich 10 g of polyvinyl alcohol (PVA) is reacted with ethylene oxide,and the weight of the resulting PVA derivative is 15 g. The PVA unitshave the formula —(CH₂CH(OH))—, and so their unit molecular weight is44. In the PVA derivative obtained as the reaction product, the —Hgroups on the original —(CH₂CH(OH))— units have become—O—(CH₂CH₂O)_(n)—H groups, and so the unit molecular weight of thereaction product is 44+44n. Because the increase in weight associatedwith the reaction is represented by 44n, the calculation is carried outas follows.

PVA/PVA derivative=44/44+440n=10g/15g

[0184] 440+440n=660

[0185] n=0.5

[0186] Hence, the molar substitution in this example is 0.5. Of course,this value merely represents the average molar substitution and does notgive any indication of, for example, the number of unreacted PVA unitson the molecule or the length of the oxyethylene groups introduced ontothe PVA by the reaction.

 α+β+γ=1

[0187] MS=0 unit MS=1 unit MS=2 units

Average MS=0+1+2/3=1

[0188] Suitable methods for introducing oxyalkylene-containing groupsonto the above polyvinyl alcohol unit-containing polymeric compoundinclude (1) reacting the polyvinyl alcohol unit-containing polymericcompound with an oxirane compound such as ethylene oxide, and (2)reacting the polyvinyl alcohol unit-containing polymeric compound with apolyoxyalkylene compound having a hydroxy-reactive substituent on theend.

[0189] In above method (1), the oxirane compound may be any one orcombination selected from among ethylene oxide, propylene oxide andglycidol.

[0190] If ethylene oxide is reacted in this case, oxyethylene chains areintroduced onto the polymeric compound as shown in the followingformula.

[0191] In the formula, the letter a is preferably from 1 to 10, and mostpreferably from 1 to 5.

[0192] If propylene oxide is reacted instead, oxypropylene chains areintroduced onto the polymeric compound as shown below.

[0193] In the formula, the letter b is preferably from 1 to 10, and mostpreferably from 1 to 5.

[0194] And if glycidol is reacted, two branched chains (1) and (2) areintroduced onto the compound, as shown below.

[0195] Reaction of a hydroxyl group on the PVA with glycidol can proceedin either of two ways: a attack or b attack.

[0196] The reaction of one glycidol molecule creates two new hydroxylgroups, each of which can in turn react with glycidol. As a result, thetwo following branched chains (1) and (2) are introduced onto thehydroxyl groups of the PVA units.

[0197] In branched chains (1) and (2), the value x+y is preferably from1 to 10, and most preferably from 1 to 5. The ratio of x to y is notparticularly specified, although x:y generally falls within a range of0.4:0.6 to 0.6:0.4.

[0198] The reaction of the polyvinyl alcohol unit-containing polymericcompound with the above oxirane compound can be carried out using abasic catalyst such as sodium hydroxide, potassium hydroxide or any ofvarious amine compounds.

[0199] The reaction of polyvinyl alcohol with glycidol is described forthe purpose of illustration. First, the reaction vessel is charged witha solvent and polyvinyl alcohol. It is not essential in this case forthe polyvinyl alcohol to dissolve in the solvent. That is, the polyvinylalcohol may be present in the solvent either in a uniformly dissolvedstate or in a suspended state. A given amount of a basic catalyst, suchas aqueous sodium hydroxide, is added and stirred for a while into thesolution or suspension, following which glycidol diluted with a solventis added. Reaction is carried out at a given temperature for a givenlength of time, after which the polyvinyl alcohol is removed. If thepolyvinyl alcohol is present within the reaction mixture in undissolvedform, it is separated off by filtration using a glass filter, forexample. If, on the other hand, the polyvinyl alcohol is dissolvedwithin the reaction mixture, it is precipitated out of solution bypouring an alcohol or other suitable precipitating agent into thereaction mixture, following which the precipitate is separated off usinga glass filter or the like. The modified polyvinyl alcohol product ispurified by dissolution in water, neutralization, and either passagethrough an ion-exchange resin or dialysis. The purified product is thenfreeze-dried, giving a dihydroxypropylated polyvinyl alcohol.

[0200] In the reaction, the molar ratio between the polyvinyl alcoholand the oxirane compound is preferably 1:10, and most preferably 1:20.

[0201] The polyoxyalkylene compound having a hydroxy-reactivesubstituent at the end used in above method (2) may be a compound ofgeneral formula (7) below

A—(R¹⁶O)_(m)—R¹⁵  (7)

[0202] In formula (7), the letter A represents a monovalent substituenthaving reactivity with hydroxyl groups. Illustrative examples includeisocyanate groups, epoxy groups, carboxyl groups, acid chloride groups,ester groups, amide groups, halogen atoms such as fluorine, bromine andchlorine, silicon-bearing reactive substituents, and other monovalentsubstituents capable of reacting with hydroxyl groups. Of these,isocyanate groups, epoxy groups, and acid chloride groups are preferredon account of their reactivity.

[0203] The carboxyl group may also be an acid anhydride. Preferred estergroups are methyl ester and ethyl ester groups. Examples of suitablesilicon-bearing reactive substituents include substituents havingterminal SiH or SiOH groups.

[0204] The hydroxy-reactive group, such as isocyanate or epoxy, may bebonded directly to the oxyalkylene group R¹⁶O or through, for example,an intervening oxygen atom, sulfur atom, carbonyl group, carbonyloxygroup, nitrogenous group (e.g., NH—, N(CH₃)—, N(C₂H₅)—) or SO₂ group.Preferably, the hydroxy-reactive group is bonded to the oxyalkylenegroup R¹⁶O through, for example, an alkylene, alkenylene or arylenegroup having 1 to 10 carbons, and especially 1 to 6 carbons.

[0205] Examples of polyoxyalkylene groups bearing this type ofsubstituent A that may be used are the products obtained by reacting apolyisocyanate compound at the hydroxyl end group on a polyoxyalkylenegroup. Isocyanate group-bearing compounds that may be used in this caseinclude compounds having two or more isocyanate groups on the molecule,such as tolylene diisocyanate, xylylene diisocyanate, naphthylenediisocyanate, diphenylmethane diisocyanate, biphenylene diisocyanate,diphenyl ether diisocyanate, tolidine diisocyanate, hexamethylenediisocyanate and isophorone diisocyanate. For example, use can be madeof compounds obtained from the following reaction.

[0206] In the formula, R¹⁶O is an oxyalkylene group of 2 to 5 carbons,examples of which include —CH₂CH₂O—, —CH₂CH₂CH₂O—, —CH₂CH(CH₃)O—,—CH₂CH(CH₂CH₃)O— and —CH₂CH₂CH₂CH₂O—. The letter m represents the numberof moles of the oxyalkylene group added. This number of added moles (m)is preferably from 1 to 100, and most preferably from 1 to 50.

[0207] Here, the polyoxyalkylene chain represented by above formula(R¹⁶O)_(m) is most preferably a polyethylene glycol chain, apolypropylene glycol chain or a polyethylene oxide (EO)/polypropyleneoxide (PO) copolymer chain. The weight-average molecular weight of thepolyoxyalkylene chain is preferably from 100 to 3,000, and mostpreferably within the range of 200 to 1,000 at which the compound isliquid at room temperature.

[0208] R¹⁵ in the above formula is a capping moiety for one end of thechain. This represents a hydrogen atom, a substituted or unsubstitutedmonovalent hydrocarbon group having 1 to 10 carbons, or a R¹⁵CO— group(wherein R¹⁵ is a substituted or unsubstituted monovalent hydrocarbongroup having 1 to 10 carbons).

[0209] Illustrative examples of R¹⁵CO— groups that may be used as thecapping moiety include those in which R¹⁵ is a substituted orunsubstituted monovalent hydrocarbon group of 1 to 10 carbons. Preferredexamples of R¹⁵ include alkyl or phenyl groups which may be substitutedwith cyano, acyl groups, benzoyl groups and cyanobenzoyl groups.

[0210] The foregoing substituted or unsubstituted monovalent hydrocarbongroups of 1 to 10 carbons are exemplified by the same groups as thosementioned above for R¹ and R². Such groups having 1 to 8 carbons areespecially preferred.

[0211] The reaction in method (2) between the above-described polyvinylalcohol unit-containing polymeric compound and the above-describedpolyoxyalkylene compound having a hydroxy-reactive substituent at theend may be carried out in the same manner as the reaction carried outwith an oxirane compound in method (1).

[0212] In the reaction, the molar ratio between the polyvinyl alcoholand the polyoxyalkylene compound having a hydroxy-reactive substituentat the end is preferably from 1:1 to 1:20, and most preferably from 1:1to 1:10.

[0213] The structure of the polymeric compound of the invention in whichoxyalkylene-containing groups have been introduced onto polyvinylalcohol units can be verified by ¹³C-NMR spectroscopy.

[0214] The extent to which the oxyalkylene chain-bearing polyvinylalcohol unit-containing polymeric compound serving as component (b) ofmatrix polymer B in the invention contains oxyalkylene groups can bedetermined in this case using various analytical techniques such as NMRand elemental analysis, although a method of determination based on theweight of the polymer charged as a reactant and the increase in weightof the polymer formed by the reaction is simple and convenient. Forexample, determination from the yield may be carried out by preciselymeasuring both the weight of the polyvinyl alcohol unit-containingpolymeric compound charged into the reaction and the weight of theoxyalkylene group-bearing polyvinyl alcohol unit-containing polymericcompound obtained from the reaction, then using this difference tocalculate the quantity of oxyalkylene chains that have been introducedonto the molecule (referred to hereinafter as the average molarsubstitution, or “MS”).

[0215] The average molar substitution serves here as an indicator of thenumber of moles of oxyalkylene groups that have been introduced onto themolecule per polyvinyl alcohol unit. In the polymeric compound of theinvention, the average molar substitution must be at least 0.3, and ispreferably at least 0.5, more preferably at least 0.7 and mostpreferably at least 1.0. No particular upper limit is imposed on theaverage molar substitution, although a value not higher than 20 ispreferred. Too low an average molar substitution may result in a failureof the ion-conductive salt to dissolve, lower ion mobility and lowerionic conductivity. On the other hand, increasing the average molarsubstitution beyond a certain level fails to yield any further change inthe solubility of the ion-conductive salt or ion mobility and is thuspointless.

[0216] Depending on its average degree of polymerization, theoxyalkylene chain-bearing polyvinyl alcohol unit-containing polymericcompound used as component (b) varies in appearance at room temperature(20° C.) from a highly viscous molasses-like liquid to a rubbery solid.The higher the average molecular weight, the more the compound, with itslow fluidity at room temperature, qualifies as a solid (albeit a soft,paste-like solid).

[0217] Regardless of its average degree of polymerization, the polymericcompound serving as component (b) is not a linear polymer. Rather, dueto the interlocking of its highly branched molecular chains, it is anamorphous polymer.

[0218] The polyvinyl alcohol derivative used as component (b) can beprepared by capping some or all of the hydroxyl groups on the molecule(these being the sum of the remaining hydroxyl groups from the polyvinylalcohol units and the hydroxyl groups on the oxyalkylene-containinggroups introduced onto the molecule), and preferably at least 10 mol %,with one or more monovalent substituent selected from among halogenatoms, substituted or unsubstituted monovalent hydrocarbon groups having1 to 10 carbons, R¹⁵CO— groups (wherein R¹⁵ is a substituted orunsubstituted monovalent hydrocarbon group of 1 to 10 carbons), R¹⁵ ₃Si-groups (R¹⁵ being as defined above), amino groups, alkylamino groups andphosphorus-containing groups.

[0219] The foregoing substituted or unsubstituted monovalent hydrocarbongroups of 1 to 10 carbons are exemplified by the same groups as thosementioned above for R¹ and R². Such groups having 1 to 8 carbons areespecially preferred.

[0220] Capping may be carried out using known techniques for introducingvarious suitable substituents onto hydroxyl end groups.

[0221] The polyvinyl alcohol derivative serving as component (b) istypically included in an amount of 0.5 to 30 wt %, and preferably 1 to20 wt %, based on the overall polymer gel electrolyte.

[0222] The polyglycidol derivative serving as component (c) of theearlier-described matrix polymer C is a compound containing units offormula (8) (referred to hereinafter as “A units”)

[0223] and units of formula (9) (referred to hereinafter as “B units”)

[0224] The ends of the molecular chains on the compound are capped withspecific substituents.

[0225] The polyglycidol can be prepared by polymerizing glycidol or3-chloro-1,2-propanediol, although it is generally advisable to carryout polymerization using glycidol as the starting material.

[0226] Known processes for carrying out such a polymerization reactioninclude (1) processes involving the use of a basic catalyst such assodium hydroxide, potassium hydroxide or any of various amine compounds;and (2) processes involving the use of a Lewis acid catalyst (see A.Dworak et al.: Macromol. Chem. Phys. 196, 1963-1970 (1995); and R.Toker: Macromolecules 27, 320-322 (1994)).

[0227] The total number of A and B units in the polyglycidol ispreferably at least two, more preferably at least six, and mostpreferably at least ten. There is no particular upper limit, although atotal number of such groups which does not exceed 10,000 is preferred.The total number of A and B units is preferably low in cases where thepolyglycidol must have the flowability of a liquid, and is preferablyhigh where a high viscosity is required.

[0228] The order of these A and B units is not regular, but random. Anycombination is possible, including, for example, -A-A-A, -A-A-B-,-A-B-A-, -B-A-A-, -A-B-B-, -B-A-B-, -B-B-A- and -B-B-B-.

[0229] The polyglycidol has a polyethylene glycol equivalentweight-average molecular weight (Mw), as determined by gel permeationchromatography (GPC), within a range of preferably 200 to 730,000, morepreferably 200 to 100,000, and most preferably 600 to 20,000.Polyglycidol having a weight-average molecular weight of up to about2,000 is a highly viscous liquid that flows at room temperature, whereaspolyglycidol with a weight-average molecular weight above 3,000 is asoft, paste-like solid at room temperature. The average molecular weightratio (Mw/Mn) is preferably 1.1 to 20, and most preferably 1.1 to 10.

[0230] Depending on its molecular weight, the polyglycidol varies inappearance at room temperature (20° C.) from a highly viscousmolasses-like liquid to a rubbery solid. The higher the molecularweight, the more the compound, with its low fluidity at roomtemperature, qualifies as a solid (albeit a soft, paste-like solid).

[0231] Regardless of how large or small its molecular weight, thepolyglycidol is not a linear polymer. Rather, due to the interlocking ofits highly branched molecular chains, it is an amorphous polymer. Thisis evident from the wide-angle x-ray diffraction pattern, which lacksany peaks indicative of the presence of crystals.

[0232] The ratio of A units to B units in the molecule is within a rangeof preferably 1/9 to 9/1, and especially 3/7 to 7/3.

[0233] Because the polyglycidol is colorless, transparent and nontoxic,it can be used in a broad range of applications, such as aelectrochemical material, including binder substances for various activematerials (e.g., binders in electroluminescent devices), as a thickener,or as an alkylene glycol substitute.

[0234] In the practice of the invention, component (c) of matrix polymerC is a polyglycidol derivative in which at least 10% of the terminalhydroxyl groups on the molecular chains of the above-describedpolyglycidol are capped with one or more type of monovalent groupselected from among halogen atoms, substituted or unsubstitutedmonovalent hydrocarbon groups, R¹⁵CO— groups (wherein R¹⁵ is asubstituted or unsubstituted monovalent hydrocarbon group), R¹⁵ ₃Si—groups (wherein R¹⁵ is as defined above), amino groups, alkylaminogroups, H(OR¹⁶)_(m)— groups (wherein R¹⁶ is an alkylene group of 2 to 5carbons, and the letter m is an integer from 1 to 100), andphosphorus-containing groups.

[0235] The foregoing substituted or unsubstituted monovalent hydrocarbongroups of 1 to 10 carbons are exemplified by the same groups as thosementioned above for R¹ and R². Such groups having 1 to 8 carbons areespecially preferred.

[0236] Capping may be carried out using known techniques for introducingvarious suitable substituents onto hydroxyl end groups.

[0237] The polyglycidol derivative serving as component (c) is typicallyincluded in an amount of 0.5 to 30 wt %, and preferably 1 to 20 wt %,based on the overall polymer gel electrolyte.

[0238] Any of the following may be used as the crosslinkable functionalgroup-bearing compound serving as component (d):

[0239] (1) an epoxy group-bearing compound in combination with acompound having two or more active hydrogens capable of reacting withthe epoxy group;

[0240] (2) an isocyanate group-bearing compound in combination with acompound having two or more active hydrogens capable of reacting withthe isocyanate group;

[0241] (3) a compound having two or more reactive double bonds.

[0242] Illustrative examples of the epoxy group-bearing compound (1)include compounds having two or more epoxy groups on the molecule, suchas sorbitol polyglycidyl ether, sorbitan polyglycidyl ether,polyglycerol polyglycidyl ether, pentaerythritol polyglycidyl ether,diglycerol polyglycidyl ether, triglycidyl tris(2-hydroxyethyl)isocyanurate, glycerol polyglycidyl ether, trimethylpropane polyglycidylether, resorcinol diglycidyl ether, 1,6-hexanediol diglycidyl ether,ethylene glycol diglycidyl ether, propylene glycol diglycidyl ether, thediglycidyl ethers of ethylene-propylene glycol copolymers,polytetramethylene glycol diglycidyl ether and adipic acid diglycidylether.

[0243] A three-dimensional network structure can be formed by reactingthe above epoxy group-bearing compound with a compound having at leasttwo active hydrogens, such as an amine, alcohol, carboxylic acid orphenol. Illustrative examples of the latter compound include polymericpolyols such as polyethylene glycol, polypropylene glycol and ethyleneglycol-propylene glycol copolymers, and also ethylene glycol,1,2-propylene glycol, 1,3-propylene glycol, 1,3-butanediol,1,4-butanediol, 1,5-pentanediol, 1,6-hexanediol,2,2-dimethyl-1,3-propanediol, diethylene glycol, dipropylene glycol,1,4-cyclohexanedimethanol, 1,4-bis(β-hydroxyethoxy)benzene andp-xylylenediol; polyamines such as phenyl diethanolamine, methyldiethanolamine and polyethyleneimine; and polycarboxylic acids.

[0244] Illustrative examples of the isocyanate group-bearing compound(2) include compounds having two or more isocyanate groups, such astolylene diisocyanate, xylylene diisocyanate, naphthylene diisocyanate,diphenylmethane diisocyanate, biphenylene diisocyanate, diphenyl etherdiisocyanate, tolidine diisocyanate, hexamethylene diisocyanate andisophorone diisocyanate.

[0245] An isocyanato-terminal polyol compound prepared by reacting theabove isocyanate compound with a polyol compound can also be used. Suchcompounds can be prepared by reacting an isocyanate such asdiphenylmethane diisocyanate or tolylene diisocyanate with one of thepolyol compounds listed below.

[0246] In this case, the stoichiometric ratio between the isocyanategroups [NCO] on the isocyanate compound and the hydroxyl groups [OH] onthe polyol compound is such as to satisfy the condition [NCO]>[OH]. Theratio [NCO]/[OH] is preferably in a range of 1.03/1 to 10/1, andespecially 1.10/1 to 5/1.

[0247] Suitable examples of the polyol compound include polymericpolyols such as polyethylene glycol, polypropylene glycol and ethyleneglycol-propylene glycol copolymers; and also ethylene glycol,1,2-propylene glycol, 1,3-propylene glycol, 1,3-butanediol,1,4-butanediol, 1,5-pentanediol, 1,6-hexanediol,2,2-dimethyl-1,3-propanediol, diethylene glycol, dipropylene glycol,1,4-cyclohexanedimethanol, 1,4-bis-(β-hydroxyethoxy)benzene,p-xylylenediol, phenyl diethanolamine, methyl diethanolamine and3,9-bis(2-hydroxy-1,1-dimethyl)-2,4,8,10-tetraoxaspiro[5,5]undecane.

[0248] Alternatively, instead of the polyol, an amine having two or moreactive hydrogens may be reacted with the isocyanate. The amine used maybe one having a primary or a secondary amino group, although a primaryamino group-bearing compound is preferred. Suitable examples includediamines such as ethylenediamine, 1,6-diaminohexane, 1,4-diaminobutaneand piperazine; polyamines such as polyethyleneamine; and amino alcoholssuch as N-methyldiethanolamine and aminoethanol. Of these, diamines inwhich the functional groups have the same level of reactivity areespecially preferred. Here again, the stoichiometric ratio between [NCO]groups on the isocyanate compound and [NH₂] and [NH] groups on the aminecompound is such as to satisfy the condition [NCO]>[NH₂]+[NH].

[0249] The above isocyanate group-bearing compound cannot by itself forma three-dimensional network structure. However, a three-dimensionalnetwork structure can be formed by reacting the isocyanate group-bearingcompound with a compound having at least two active hydrogens, such asan amine, alcohol, carboxylic acid or phenol. Illustrative examples ofsuch compounds having at least two active hydrogens include polymericpolyols such as polyethylene glycol, polypropylene glycol and ethyleneglycol-propylene glycol copolymers, and also ethylene glycol,1,2-propylene glycol, 1,3-propylene glycol, 1,3-butanediol,1,4-butanediol, 1,5-pentanediol, 1,6-hexanediol,2,2-dimethyl-1,3-propanediol, diethylene glycol, dipropylene glycol,1,4-cyclohexanedimethanol, 1,4-bis(β-hydroxyethoxy)benzene andp-xylylenediol; polyamines such as phenyl diethanolamine, methyldiethanolamine and polyethyleneimine; and polycarboxylic acids.

[0250] Illustrative examples of the above reactive double bond-bearingcompound (3) which may be used as the crosslinkable functionalgroup-bearing compound serving as component (d) include compoundscontaining two or more reactive double bonds, such as divinylbenzene,divinylsulfone, allyl methacrylate, ethylene glycol dimethacrylate,diethylene glycol dimethacrylate, triethylene glycol dimethacrylate,polyethylene glycol dimethacrylate (average molecular weight, 200 to1,000), 1,3-butylene glycol dimethacrylate, 1,6-hexanedioldimethacrylate, neopentyl glycol dimethacrylate, polypropylene glycoldimethacrylate (average molecular weight, 400),2-hydroxy-1,3-dimethacryloxypropane,2,2-bis[4(methacryloxyethoxy)phenyl]propane,2,2-bis[4-(methacryloxyethoxy-diethoxy)phenyl]propane,2,2-bis[4-(methacryloxyethoxy-polyethoxy)phenyl]propane, ethylene glycoldiacrylate, diethylene glycol diacrylate, triethylene glycol diacrylate,polyethylene glycol diacrylate (average molecular weight, 200 to 1,000),1,3-butylene glycol diacrylate, 1,6-hexanediol diacrylate, neopentylglycol diacrylate, polypropylene glycol diacrylate (average molecularweight, 400), 2-hydroxy-1,3-diacryloxypropane,2,2-bis[4-(acryloxyethoxy)phenyl]propane,2,2-bis[4-(acryloxyethoxy-diethoxy)phenyl]propane,2,2-bis[4-(acryloxyethoxy-polyethoxy)phenyl] propane, trimethylolpropanetriacrylate, trimethylolpropane trimethacrylate, tetramethylolmethanetriacrylate, tetramethylolmethane tetraacrylate, tricyclodecanedimethanol acrylate, hydrogenated dicyclopentadiene diacrylate,polyester diacrylate, polyester dimethacrylate, and the above-describedunsaturated polyurethane compounds (I)

[0251] If necessary, a compound containing an acrylic or methacrylicgroup may be added. Examples of such compounds include acrylates andmethacrylates such as glycidyl methacrylate, glycidyl acrylate andtetrahydrofurfuryl methacrylate, as well as methacryloyl isocyanate,2-hydroxymethylmethacrylic acid and N,N-dimethylaminoethylmethacrylicacid. Other reactive double bond-containing compounds may be added aswell, such as acrylamides (e.g., N-methylolacrylamide,methylenebisacrylamide, diacetoneacrylamide), and vinyl compounds suchas vinyloxazolines and vinylene carbonate.

[0252] Here too, in order to form a three-dimensional network structure,a compound having at least two reactive double bonds must be added. Thatis, a three-dimensional network structure cannot be formed with onlycompounds such as methyl methacrylate that have but a single reactivedouble bond. Some addition of a compound bearing at least two reactivedouble bonds is required.

[0253] Of the aforementioned reactive double bond-bearing compounds,especially preferred reactive monomers include the above-describedunsaturated polyurethane compounds (I) and polyoxyalkylenecomponent-bearing diesters of general formula (10) below. The use ofthese in combination with a polyoxyalkylene component-bearing monoesterof general formula (11) below is recommended.

[0254] In formula (10), R¹⁷, R¹⁸ and R¹⁹ are each independently ahydrogen atom or an alkyl group having 1 to 6 carbons, and preferably 1to 4 carbons, such as methyl, ethyl, n-propyl, i-propyl, n-butyl,i-butyl, s-butyl and t-butyl; and X and Y satisfy the condition X≧1 andY≧0 or the condition X≧0 and Y≧1. The sum X+Y is preferably no higherthan 100, and especially from 1 to 30. R¹⁷, R¹⁸ and R¹⁹ are mostpreferably methyl, ethyl, n-propyl, i-propyl, n-butyl, i-butyl, s-butylor t-butyl.

[0255] In formula (11), R²⁰, R²¹ and R²² are each independently ahydrogen atom or an alkyl group having 1 to 6 carbons, and preferably 1to 4 carbons, such as methyl, ethyl, n-propyl, i-propyl, n-butyl,i-butyl, s-butyl and t-butyl; and A and B satisfy the condition A≧1 andB≧0 or the condition A≧0 and B≧1. The sum A+B is preferably no higherthan 100, and especially from 1 to 30. R²⁰, R²¹ and R²² are mostpreferably methyl, ethyl, n-propyl, i-propyl, n-butyl, i-butyl, s-butylor t-butyl.

[0256] Typically, the above-described unsaturated polyurethane compound(I) or polyoxyalkylene component-bearing diester and the polyoxyalkylenecomponent-bearing monoester are heated or exposed to a suitable form ofradiation, such as electron beams, microwaves or radio-frequencyradiation, within the polymer electrolyte composition, or a mixture ofthe compounds is heated, so as to form the three-dimensional networkstructure.

[0257] The three-dimensional network structure can generally be formedby reacting only the above-described unsaturated polyurethane compound(I) or the polyoxyalkylene component-bearing diester. However, asalready noted, the addition of a polyoxyalkylene component-bearingmonoester, which is a monofunctional monomer, to the unsaturatedpolyurethane compound or the polyoxyalkylene component-bearing diesteris preferred because such addition introduces polyoxyalkylene branchedchains onto the three-dimensional network.

[0258] No particular limitation is imposed on the relative proportionsof the unsaturated polyurethane compound or polyoxyalkylenecomponent-bearing diester and the polyoxyalkylene component-bearingmonoester, although a weight ratio (unsaturated polyurethane compound orpolyoxyalkylene component-bearing diester)/(polyoxyalkylenecomponent-bearing monoester) within a range of 0.2 to 10, and especially0.5 to 5, is preferred because this enhances film strength.

[0259] The crosslinkable functional group-bearing compound serving ascomponent (d) is typically included in an amount of at least 1 wt %,preferably 5 to 40 wt %, and most preferably 10 to 20 wt %, based on theoverall polymer gel electrolyte.

[0260] The matrix polymer containing component (a), (b) or (c) incombination with component (d), when heated or exposed to a suitableform of radiation, such as electron beams, microwaves or radio-frequencyradiation, forms a semi-interpenetrating polymer network structure inwhich molecular chains of a polymer of component (a), (b) or (c) areinterlocked with the three-dimensional network structure of a polymerformed by the reaction (polymerization) of the crosslinkable functionalgroup-bearing compound serving as component (d).

[0261] Thermoplastic resins containing units of general formula (3)below may be used as the above-mentioned type (III) matrix polymer.

[0262] In the formula, the letter r is an integer from 3 to 5, and theletter s is an integer ≧5.

[0263] Such a thermoplastic resin is preferably a thermoplasticpolyurethane resin prepared by reacting (E) a polyol compound with (F) apolyisocyanate compound and (G) a chain extender. Suitable thermoplasticpolyurethane resins include not only polyurethane resins having urethanelinkages, but also polyurethane-urea resins having both urethanelinkages and urea linkages.

[0264] The polyol compound serving as component (E) above is preferablyone prepared by the dehydration or dealcoholation of any of compounds(i) to (vi) below, and most preferably a polyester polyol, a polyesterpolyether polyol, a polyester polycarbonate polyol, a polycaprolactonepolyol, or a mixture thereof:

[0265] (i) polyester polyols prepared by the ring-opening polymerizationof one or more cyclic ester (lactone);

[0266] (ii) polyester polyols prepared by reacting at least one of theabove polyester polyols obtained by the ring-opening polymerization of acyclic ester (lactone) with at least one carboxylic acid and at leastone compound selected from the group consisting of dihydric aliphaticalcohols, carbonate compounds, polycarbonate polyols and polyetherpolyols;

[0267] (iii) polyester polyols prepared by reacting at least onecarboxylic acid with at least one dihydric aliphatic alcohol;

[0268] (iv) polyester polycarbonate polyols prepared by reacting atleast one carboxylic acid with at least one polycarbonate polyol;

[0269] (v) polyester polyether polyols prepared by reacting at least onecarboxylic acid with at least one polyether polyol; and

[0270] (vi) polyester polyols prepared by reacting at least onecarboxylic acid with two or more compounds selected from the groupconsisting of dihydric aliphatic alcohols, polycarbonate polyols andpolyether polyols.

[0271] Examples of suitable cyclic esters (lactones) includeγ-butyrolactone, δ-valerolactone and ε-caprolactone.

[0272] Examples of suitable carboxylic acids include linear aliphaticdicarboxylic acids having 5 to 14 carbons, such as glutaric acid, adipicacid, pimelic acid, suberic acid, azelaic acid, sebacic acid anddodecanedioic acid; branched aliphatic dicarboxylic acids having 5 to 14carbons, such as 2-methylsuccinic acid, 2-methyladipic acid,3-methyladipic acid, 3-methylpentanedioic acid, 2-methyloctanedioicacid, 3,8-dimethyldecanedioic acid and 3,7-dimethyldecanedioic acid;aromatic dicarboxylic acids such as terephthalic acid, isophthalic acidand o-phthalic acid; and ester-forming derivatives thereof. Any one orcombinations of two or more of the above may be used. Of these, linearor branched aliphatic dicarboxylic acids having 5 to 14 carbons arepreferred. The use of adipic acid, azelaic acid or sebacic acid isespecially preferred.

[0273] Examples of suitable divalent aliphatic alcohols include linearaliphatic diols of 2 to 14 carbons, such as ethylene glycol,1,3-propanediol, 1,4-butanediol, 1,5-pentanediol, 1,6-hexanediol,1,7-heptanediol, 1,8-octanediol, 1,9-nonanediol and 1,10-decanediol;branched aliphatic diols of 3 to 14 carbons, including2-methyl-1,3-propanediol, neopentyl glycol, 3-methyl-1,5-pentanediol and2-methyl-1,8-octanediol; and alicyclic diols such ascyclohexanedimethanol and cyclohexanediol. Any one or combinations oftwo or more of the above may be used. Of these, branched or linearaliphatic diols of 4 to 10 carbons are preferred, and3-methyl-1,5-pentanediol is especially preferred.

[0274] Examples of suitable carbonate compounds include dialkylcarbonates such as dimethyl carbonate and diethyl carbonate, alkylenecarbonates such as ethylene carbonate, and diaryl carbonates such asdiphenyl carbonate.

[0275] Suitable polycarbonate polyols include those prepared by adealcoholation reaction between a polyhydric alcohol and one or more ofthe above carbonate compounds. Illustrative examples of the polyhydricalcohol include ethylene glycol, 1,3-propanediol, 1,4-butanediol,1,5-pentanediol, 1,6-hexanediol, 1,7-heptanediol, 1,8-octanediol,1,9-nonanediol, 1,10-decanediol, diethylene glycol and1,4-cyclohexanedimethanol.

[0276] Suitable polyether polyols include polyethylene glycol,polypropylene glycol, ethylene oxide/propylene oxide copolymers andpolyoxytetramethylene glycol. Any one or combinations of two or more ofthese may be used.

[0277] The polyol compound serving as component (E) has a number-averagemolecular weight of preferably 1,000 to 5,000, and most preferably 1,500to 3,000. A polyol compound having too small a number-average molecularweight may lower the physical properties of the resulting thermoplasticpolyurethane resin film, such as the heat resistance and tensileelongation. On the other hand, too large a number-average molecularweight increases the viscosity during synthesis, which may lower theproduction stability of the thermoplastic polyurethane resin beingprepared. The number-average molecular weights used here in connectionwith polyol compounds are calculated based on the hydroxyl valuesmeasured in accordance with JIS K1577.

[0278] Illustrative examples of the polyisocyanate compound serving asabove component (F) include aromatic diisocyanates such as tolylenediisocyanate, 4,4′-diphenylmethane diisocyanate, p-phenylenediisocyanate, 1,5-naphthylene diisocyanate,3,3′-dichloro-4,4′-diphenylmethane diisocyanate and xylylenediisocyanate; and aliphatic or alicyclic diisocyanates such ashexamethylene diisocyanate, isophorone diisocyanate,4,4′-dicyclohexylmethane diisocyanate and hydrogenated xylylenediisocyanate.

[0279] The chain extender serving as above component (G) is preferably alow-molecular-weight compound having a molecular weight of not more than300 and bearing two active hydrogen atoms capable of reacting withisocyanate groups.

[0280] Illustrative examples of such low-molecular-weight compoundsinclude aliphatic diols such as ethylene glycol, diethylene glycol,propylene glycol, 1,3-propanediol, 1,4-butanediol, 1,5-pentanediol,1,6-hexanediol, 1,7-heptanediol, 1,8-octanediol and 1,9-nonanediol;aromatic or alicyclic diols such as 1,4-bis(β-hydroxyethoxy)benzene,1,4-cyclohexanediol, bis(β-hydroxyethyl) terephthalate and xylyleneglycol; diamines such as hydrazine, ethylenediamine,hexamethylenediamine, propylenediamine, xylylenediamine,isophoronediamine, piperazine, piperazine derivatives, phenylenediamineand tolylenediamine; and amino alcohols such as adipoyl hydrazide andisophthaloyl hydrazide. Any one or combinations of two or more of thesemay be used.

[0281] In preparing a thermoplastic polyurethane resin for use in theinvention, it is advantageous to react components (E) to (G) in thefollowing proportions:

[0282] (E) 100 parts by weight of the polyol compound;

[0283] (F) 5 to 200 parts by weight, and preferably 20 to 100 parts byweight, of the polyisocyanate compound;

[0284] (G) 1 to 200 parts by weight, and preferably 5 to 100 parts byweight, of the chain extender.

[0285] The thermoplastic resin (III) is typically included in an amountof 0.5 to 30 wt %, and preferably 1 to 20 wt %, based on the overallpolymer gel electrolyte.

[0286] The thermoplastic resin has a swelling ratio, as determined fromthe formula indicated below, within a range of 150 to 800%, preferably250 to 500%, and most preferably 250 to 400%.${{Swelling}\quad {ratio}\quad (\%)} = {\frac{\begin{matrix}{{{weight}\quad {in}\quad {grams}\quad {of}\quad {swollen}},} \\{{ion}\text{-}{conductive}\quad {thermoplastic}} \\{{resin}\quad {composition}\quad {after}\quad 24\text{-}{hour}} \\{{immersion}\quad {in}\quad {electrolyte}\quad {solution}} \\{{at}\quad 20{^\circ}\quad {C.\quad (g)}}\end{matrix}}{\begin{matrix}{{weight}\quad {in}\quad {grams}\quad {of}\quad {thermoplastic}} \\{{resin}\quad {before}\quad {immersion}\quad {in}} \\{{electrolyte}\quad {solution}\quad (g)}\end{matrix}} \times 100}$

[0287] Illustrative examples of fluoropolymer materials that may be usedas the above-mentioned type (IV) matrix polymer include polyvinylidenefluoride (PVDF), vinylidene fluoride-hexafluoropropylene (HFP) copolymer(P(VDF-HFP)), vinylidene fluoride-chlorotrifluoroethylene (CTFE)copolymer (P(VDF-CTFE)), vinylidene fluoride-hexafluoropropylenefluororubber (P(VDF-HFP)), vinylidenefluoride-tetrafluoroethylene-hexafluoropropylene fluororubber(P(VDF-TFE-HFP)) and vinylidenefluoride-tetrafluoroethylene-perfluoro(alkyl vinyl ether) fluororubber.The fluoropolymer has a vinylidene fluoride content of preferably atleast 50 wt %, and most preferably at least 70 wt %. The upper limit inthe vinylidene fluoride content of the fluoropolymer is preferably about97 wt %. Of the above fluoropolymers, the use of polyvinylidene fluoride(PVDF), a copolymer of vinylidene fluoride and hexafluoropropylene(P(VDF-HFP)), or a copolymer of vinylidene fluoride andchlorotrifluoroethylene (P(VDF—CTFE)) is preferred.

[0288] The fluoropolymer typically has a weight-average molecular weightof at least 500,000, preferably from 500,000 to 2,000,000, and mostpreferably from 500,000 to 1,500,000. Too low a weight-average molecularweight may result in an excessive decline in physical strength.

[0289] The fluoropolymer material is typically included in an amount of0.5 to 30 wt %, and preferably 1 to 20 wt %, based on the overallpolymer gel electrolyte.

Secondary Battery of the Invention

[0290] The secondary battery of the invention includes a positiveelectrode, a negative electrode and an electrolyte. The polymer gelelectrolyte of the invention serves as the battery electrolyte.

[0291] The positive electrode is produced by coating one or both sidesof a positive electrode current collector with a positive electrodebinder composition composed primarily of a binder resin and a positiveelectrode active material. The positive electrode binder compositioncomposed primarily of a binder resin and a positive electrode activematerial is melted and blended, then extruded as a film to form apositive electrode.

[0292] The binder resin may be any of the above-described matrixpolymers (I) to (IV) used in the polymer gel electrolytes of theinvention, or another binder resin commonly employed as an electrodebinder resin in secondary batteries. Having the binder resin be composedof the same polymeric material as the matrix polymer in the polymer gelelectrolyte of the invention is preferable for lowering the internalresistance of the battery.

[0293] The positive electrode current collector may be made of asuitable material such as stainless steel, aluminum, titanium, tantalumor nickel. Of these, aluminum is especially preferred both in terms ofperformance and cost. The current collector used may be in any ofvarious forms, including foil, expanded metal, sheet, foam, wool, or athree-dimensional structure such as a net.

[0294] The positive electrode active material is selected as appropriatefor the electrode application, the type of battery and otherconsiderations. For instance, examples of positive electrode activematerials that are suitable for use in the positive electrode of alithium secondary cell include group I metal compounds such as CuO,Cu₂O, Ag₂O, CuS and CuSO₂; group IV metal compounds such as TiS, SiO₂and SnO; group V metal compounds such as V₂O₅, V₆O₁₃, VO_(X), Nb₂O₅,Bi₂O₃ and Sb₂O₃; group VI metal compounds such as CrO₃, Cr₂O₃, MoO₃,MoS₂, WO₃ and SeO₂; group VII metal compounds such as MnO₂ and Mn₂O₄;group VIII metal compounds such as Fe₂O₃, FeO, Fe₃O₄, Ni₂O₃, NiO andCoO₂; and conductive polymeric compounds such as polypyrrole,polyaniline, poly(p-phenylene), polyacetylene and polyacene.

[0295] Suitable positive electrode active materials that may be used inlithium ion secondary cells include chalcogen compounds capable ofadsorbing and releasing lithium ions, and lithium ion-containingchalcogen compounds.

[0296] Examples of such chalcogen compounds capable of adsorbing andreleasing lithium ions include FeS₂, TiS₂, MoS₂, V₂O₅, V₆O₁₃ and MnO₂.

[0297] Specific examples of lithium ion-containing chalcogen compoundsinclude LiCoO₂, LiMnO₂, LiMn₂O₄, LiMo₂O₄, LIV₃O₈, LiNiO₂ andLi_(x)Ni_(y)M_(1-y)O₂ (wherein M is at least one metal element selectedfrom among cobalt, manganese, titanium, chromium, vanadium, aluminum,tin, lead and zinc; 0.05≦x ≦1.10; and 0.5≦y ≦1.0).

[0298] In addition to the binder resin and the positive electrode activematerial described above, if necessary, the binder composition for thepositive electrode may include also an electrically conductive material.Illustrative examples of the conductive material include carbon black,Ketjenblack, acetylene black, carbon whiskers, carbon fibers, naturalgraphite, and artificial graphite.

[0299] The positive electrode binder composition of the inventiontypically includes 1,000 to 5,000 parts by weight, and preferably 1,200to 3,500 parts by weight, of the positive electrode active material and20 to 500 parts by weight, and preferably 50 to 400 parts by weight, ofthe conductive material per 100 parts by weight of the binder resin.

[0300] Because the positive electrode binder composition of theinvention provides good bonding of the positive electrode activematerial particles and has a high adhesion to the positive electrodecurrent collector, a positive electrode can be produced with theaddition of only a small amount of binder resin. The high ionicconductivity of the binder composition when swollen with electrolytesolution lowers the internal resistance of the battery.

[0301] The above-described positive electrode binder composition isgenerally used together with a dispersant in the form of a paste.Suitable dispersants include polar solvents such asN-methyl-2-pyrrolidone, dimethylformamide, dimethylacetamide anddimethylsulfamide. The dispersant is typically added in an amount ofabout 30 to 300 parts by weight per 100 parts by weight of the positiveelectrode binder composition.

[0302] No particular limitation is imposed on the method of shaping thepositive electrode as a thin film, although it is preferable to applythe composition by a suitable means such as roller coating with anapplicator roll, screen coating, doctor blade coating, spin coating orbar coating so as to form an active material layer having a uniformthickness when dry of 10 to 200 μm, and especially 50 to 150 μm. Whenthe matrix polymer of the inventive polymer gel electrolyte is used asthe positive electrode binder resin, the positive electrode may befabricated by first shaping the electrode as described above, thenimmersing it in the plasticizer of the invention to induce swelling.

[0303] The negative electrode is produced by coating one or both sidesof a negative electrode current collector with a negative electrodebinder composition composed primarily of a binder resin and a negativeelectrode active material. The same binder resin may be used as in thepositive electrode. The negative electrode binder composition composedprimarily of a binder resin and a negative electrode active material ismelted and blended, then extruded as a film to form a negativeelectrode.

[0304] The negative electrode current collector may be made of asuitable material such as copper, stainless steel, titanium or nickel.Of these, copper is especially preferred both in terms of performanceand cost. The current collector used may be in any of various forms,including foil, expanded metal, sheet, foam, wool, or athree-dimensional structure such as a net.

[0305] The negative electrode active material is selected as appropriatefor the electrode application, the type of battery and otherconsiderations. Active materials suitable for use in the negativeelectrode of a lithium secondary cell, for example, include alkalimetals, alkali metal alloys, carbonaceous materials, and the samematerials as mentioned above for the positive electrode active material.

[0306] Examples of suitable alkali metals include lithium, sodium andpotassium. Examples of suitable alkali metal alloys include Li—Al,Li—Mg, Li—Al—Ni, Na—Hg and Na—Zn.

[0307] Examples of suitable carbonaceous materials include graphite,carbon black, coke, glassy carbon, carbon fibers, and sintered bodiesobtained from any of these.

[0308] In a lithium ion secondary cell, use may be made of a materialwhich reversibly holds and releases lithium ions. Suitable carbonaceousmaterials capable of reversibly adsorbing and releasing lithium ionsinclude non-graphitizable carbonaceous materials and graphite materials.Specific examples include pyrolytic carbon, coke (e.g., pitch coke,needle coke, petroleum coke), graphites, glassy carbons, fired organicpolymeric materials (materials such as phenolic resins or furan resinsthat have been carbonized by firing at a suitable temperature), carbonfibers, and activated carbon. Use can also be made of materials capableof reversibly adsorbing and releasing lithium ions, including polymerssuch as polyacetylene and polypyrrole, and oxides such as SnO₂.

[0309] In addition to the binder resin and the negative electrode activematerial described above, if necessary, the binder composition for thenegative electrode may include also a conductive material. Illustrativeexamples of the conductive material include carbon black, Ketjen black,acetylene black, carbon whiskers, carbon fibers, natural graphite, andartificial graphite.

[0310] The negative electrode binder composition typically includes 500to 1,700 parts by weight, and preferably 700 to 1,300 parts by weight,of the negative electrode active material and 0 to 70 parts by weight,and preferably 0 to 40 parts by weight, of the conductive material per100 parts by weight of the binder resin.

[0311] The above-described negative electrode binder composition isgenerally used together with a dispersant in the form of a paste.Suitable dispersants include polar solvents such asN-methyl-2-pyrrolidone, dimethylformamide, dimethylacetamide anddimethylsulfamide. The dispersant is typically added in an amount ofabout 30 to 300 parts by weight per 100 parts by weight of the negativeelectrode binder composition.

[0312] No particular limitation is imposed on the method of shaping thenegative electrode as a thin film, although it is preferable to applythe composition by a suitable means such as roller coating with anapplicator roll, screen coating, doctor blade coating, spin coating orbar coating so as to form an active material layer having a uniformthickness when dry of 10 to 200 μm, and especially 50 to 150 μm. Whenthe matrix polymer of the inventive polymer gel electrolyte is used asthe negative electrode binder resin, the negative electrode may befabricated by first shaping the electrode as described above, thenimmersing it in the plasticizer of the invention to induce swelling.

[0313] The separator disposed between the resulting positive andnegative electrodes is preferably (1) a separator prepared byimpregnating a separator base with a polymer electrolyte solution, thencarrying out a chemical reaction to effect curing, or (2) theabove-described polymer gel electrolyte of the invention.

[0314] Suitable examples of the separator base used in the first type ofseparator (1) include fluoropolymers, polyethers such as polyethyleneoxide and polypropylene oxide, polyolefins such as polyethylene andpolypropylene, polyacrylonitrile, polyvinylidene chloride, polymethylmethacrylate, polymethyl acrylate, polyvinyl alcohol,polymethacrylonitrile, polyvinyl acetate, polyvinyl pyrrolidone,polyethyleneimine, polybutadiene, polystyrene, polyisoprene,polyurethane and derivatives of any of the above polymers, as well ascellulose, paper and nonwoven fabric. These may be used singly or ascombinations of two or more thereof. A fluoropolymer is especiallypreferred.

[0315] Fluoropolymers that may be used include the fluoropolymermaterials described above as type (IV) matrix polymers.

[0316] A filler may be added to the separator base. Any suitable fillerwhich forms, together with the polymer making up the separator, a matrixhaving at the filler-polymer interfaces fine pores in which theelectrolyte solution can be impregnated may be used without particularlimitation. The filler may be either an inorganic or organic material,and can have a broad range of physical characteristics such as particleshape and size, density and surface state. Exemplary fillers includeboth inorganic powders such as various oxides, carbonates and sulfates(e.g., silicon dioxide, titanium oxide, aluminum oxide, zinc oxide,calcium carbonate, calcium sulfate, tin oxide, chromium oxide, ironoxide, magnesium oxide, magnesium carbonate and magnesium sulfate),carbides (e.g., silicon carbide, calcium carbide) and nitrides (e.g.,silicon nitride, titanium nitride); and organic powders composed ofvarious types of polymer particles that do not form a compatible mixturewith the polymer matrix making up the separator.

[0317] No particular limitation is imposed on the particle size of thefiller, although the particle size is preferably not more than 10 μm,more preferably from 0.005 to 1 μm, and most preferably from 0.01 to 0.8μm. The amount in which the filler is added to the polymer variesdepending on the type of polymer used and the type of filler, althoughthe addition of 5 to 100 parts by weight, and especially 30 to 100 partsby weight, of filler per 100 parts by weight of the polymer ispreferred.

[0318] Secondary batteries according to the invention are assembled bystacking, fan-folding or winding a cell assembly composed of thepositive electrode, the negative electrode, and the separatortherebetween, each of which components is prepared as described above,and placing the cell assembly within a battery housing such as a batterycan or a laminate pack. The cell assembly is then filled with thepolymer electrolyte solution of the invention, and a chemical reactionis carried out to effect curing, following which the battery housing ismechanically sealed if it is a can or heat-sealed if it is a laminatepack.

[0319] The resulting secondary batteries of the invention can beoperated at a high capacity and a high current without compromisingtheir outstanding performance characteristics, such as an excellentcharge/discharge efficiency, high energy density, high output densityand long life. The batteries thus are highly suitable in a broad rangeof applications, particularly as lithium secondary cells and lithium ionsecondary cells.

[0320] The secondary batteries according to the invention, such aslithium secondary cells and lithium ion secondary cells, are well-suitedfor use in a broad range of applications, including main power suppliesand memory backup power supplies for portable electronic equipment suchas camcorders, notebook computers, mobile phones and what are known as“personal handyphone systems” (PHS) in Japan, uninterruptible powersupplies for equipment such as personal computers, in transport devicessuch as electric cars and hybrid cars, and together with solar cells asenergy storage systems for solar power generation.

Electrical Double-Layer Capacitor of the Invention

[0321] The electrical double-layer capacitor of the invention includes apair of polarizable electrodes and an electrolyte between thepolarizable electrodes. The polymer gel electrolyte of the inventionserves as the electrolyte.

[0322] The polarizable electrodes are made of a current collector coatedwith a polarizable electrode binder composition composed primarily of abinder resin and activated carbon. The polarizable electrode bindercomposition is melted and blended, then extruded as a film to form thepolarizable electrodes.

[0323] The binder resin may be any of the above-described matrixpolymers (I) to (IV) used in the polymer gel electrolytes of theinvention, or another binder resin commonly employed as an electrodebinder resin in electrical double-layer capacitors. Having the binderresin be the same polymeric material as the matrix polymer in thepolymer gel electrolyte of the invention is preferable for lowering theinternal resistance of the battery.

[0324] Exemplary activated carbons include those manufactured fromplant-based materials such as wood, sawdust, coconut shells and pulpspent liquor; fossil fuel-based materials such as coal and petroleumfuel oil, as well as fibers spun from coal or petroleum-based pitchobtained by the thermal cracking of such fossil fuel-based materials orfrom tar pitch; and synthetic polymers, phenolic resins, furan resins,polyvinyl chloride resins, polyvinylidene chloride resins, polyimideresins, polyamide resins, liquid-crystal polymers, plastic waste andreclaimed tire rubber. These starting materials are carbonized, thenactivated.

[0325] The activated carbon is preferably in the form of a finelydivided powder prepared by subjecting a mesophase pitch-based carbonmaterial, a polyacrylonitrile-based carbon material, a gas phase-growncarbon material, a rayon-based carbon material or a pitch-based carbonmaterial to alkali activation with an alkali metal compound, thengrinding the activated carbon material. It is especially preferable touse as the fibrous carbonaceous material a mesophase pitch carbonmaterial, a polyacrylonitrile-based carbon material, a gas phase-growncarbon material, a rayon-based carbon material or a pitch-based carbonmaterial.

[0326] The use of an activated carbon having a pore size distribution,as determined from a nitrogen adsorption isotherm, in which pores with aradius of up to 10 Å account for at most 70% of the total pore volumemakes it possible to obtain activated carbon with an optimal pore sizedistribution when a nonaqueous electrolyte solution, and especially anorganic electrolyte solution, is used. The organic electrolyte solutionmolecules penetrate fully to the interior of the pores, allowing cationsor anions to adsorb efficiently to the surface of the activated carbonand form an electrical double layer, thus making it possible to store ahigh level of electrical energy.

[0327] The pore size distribution of the activated carbon, as determinedfrom a nitrogen adsorption isotherm, is measured by the continuous flowmethod using nitrogen gas after vacuum outgassing the activated carbonsample. The volume (cc/g) of pores having a radius larger than 10 Å iscomputed from a desorption isotherm obtained by BJH pore size analysisfrom a pore distribution plot. The volume (cc/g) of pores with a radiusup to 10 Å is computed from an adsorption isotherm obtained by the MPprocedure from an MP plot.

[0328] In the activated carbon, the volume of pores having a radius upto 10 Å, as determined from a nitrogen adsorption isotherm, accounts forat most 70%, preferably up to 50%, more preferably up to 30%, and mostpreferably from 0 to 30%, of the total pore volume. If the volume ofpores having a radius of up to 10 Å is too great, the overall porevolume of the activated carbon becomes too large and the capacitance perunit volume too small.

[0329] The most common pore radius in the pore size distribution of theactivated carbon, as determined from a nitrogen adsorption isotherm, ispreferably 15 to 500 Å, more preferably 20 to 200 Å, and most preferably50 to 120 Å. Moreover, in the activated carbon, preferably at least 50%,more preferably at least 60%, even more preferably at least 70%, andmost preferably at least 80%, of the pores with a radius greater than 10Å have a pore radius within a range of 20 to 400 Å. The proportion ofpores with a radius greater than 10 Å which have a radius within a rangeof 20 to 400 Å may even be 100%.

[0330] In addition to satisfying the foregoing pore radius conditions,it is advantageous for the activated carbon to have a specific surfacearea, as measured by the nitrogen adsorption BET method, of 1 to 500m²/g, preferably 20 to 300 m²/g, more preferably 20 to 200 m²/g, evenmore preferably 20 to 150 m²/g, and most preferably 50 to 150 m²/g. Ifthe specific surface area of the activated carbon is too small, thesurface area of the activated carbon on which the electrical doublelayer forms becomes smaller than desirable, resulting in a lowcapacitance. On the other hand, if the specific surface area is toolarge, the number of micropores and sub-micropores in the activatedcarbon which are unable to adsorb ionic molecules increases, in additionto which the electrode density decreases, and with it, the capacitance.

[0331] The activated carbon has a cumulative average particle size aftergrinding of preferably at most 20 μm, more preferably at most 10 μm,even more preferably at most 5 μm, and most preferably 0.1 to 5 μm. Itis especially advantageous for the activated carbon to be in the form offine particles having a cumulative average particle size of up to 5 μm,and most preferably 0.1 to 5 μm, which have been formed by subjectingmesophase pitch-based carbon fibers to alkali activation, then grindingthe activated fibers. “Cumulative average particle size,” as usedherein, refers to the particle size at the 50% point (median size) onthe cumulative curve, based on a value of 100% for the total volume ofthe powder mass, when the particle size distribution of the finelydivided activated carbon is determined.

[0332] Subjecting the activated carbon to alkali activation followed bygrinding allows the cumulative average particle size to be made evensmaller. This makes it possible to closely pack the activated carboninto polarizable electrodes for electrical double-layer capacitors, andthereby raise the electrode density. Moreover, compared with fibrousactivated carbon, an electrode coating paste composed of the resultingmaterial can be more readily applied to a current collector andpress-formed to easily fabricate electrodes of uniform thickness.

[0333] The amount of activated carbon included in the binder compositionfor polarizable electrodes is 500 to 10,000 parts by weight, andpreferably 1,000 to 4,000 parts by weight, per 100 parts by weight ofthe binder resin. The addition of too much activated carbon may lowerthe bond strength of the binder composition, resulting in poor adhesionto the current collector. On the other hand, too little activated carbonmay have the effect of increasing the electrical resistance, and thuslowering the capacitance, of the polarizable electrodes produced withthe composition.

[0334] In addition to the binder resin and the activated carbondescribed above, if necessary, the binder composition for polarizableelectrodes may include also a conductive material.

[0335] The conductive material may be any suitable material capable ofconferring electrical conductivity to the binder composition forpolarizable electrodes. Illustrative examples include carbon black,Ketjen black, acetylene black, carbon whiskers, carbon fibers, naturalgraphite, artificial graphite, titanium oxide, ruthenium oxide, andmetallic fibers such as aluminum and nickel. Any one or combinations oftwo or more thereof may be used. Of these, Ketjen black and acetyleneblack, which are both types of carbon black, are preferred. The averageparticle size of the conductive material powder is preferably 10 to 100nm, and especially 20 to 40 nm.

[0336] The conductive material is included in an amount of preferably 0to 300 parts by weight, and especially 50 to 200 parts by weight, per100 parts by weight of the binder resin. The presence of too muchconductive material in the binder composition reduces the proportion ofactivated carbon, which may lower the capacitance of polarizableelectrodes obtained using the composition. On the other hand, too littleconductive material may fail to confer adequate electrical conductivity.

[0337] The binder composition for polarizable electrodes is generallyused together with a diluting solvent in the form of a paste. Suitablediluting solvents include N-methyl-2-pyrrolidone, acetonitrile,tetrahydrofuran, acetone, methyl ethyl ketone, 1,4-dioxane and ethyleneglycol dimethyl ether. The diluting solvent is typically added in anamount of about 30 to 300 parts by weight per 100 parts by weight of thebinder composition.

[0338] No particular limitation is imposed on the method for shaping thepolarizable electrodes as thin films, although it is preferable to applythe composition by a suitable means such as roller coating with anapplicator roll, screen coating, doctor blade coating, spin coating orbar coating so as to form an activated carbon layer of a uniformthickness after drying of 10 to 500 μm, and especially 50 to 400 μm.When the matrix polymer in the polymer gel electrolyte of the inventionis used also as the binder resin for the polarizable electrodes, oncethe polarizable electrodes have been formed as described above, they maybe immersed in the plasticizer of the invention to effect swelling andthus give the finished polarizable electrodes.

[0339] The separator disposed between the resulting pair of polarizableelectrodes is preferably (1) a separator prepared by impregnating aseparator base with a polymer electrolyte solution, then carrying out achemical reaction to effect curing, or (2) the above-described polymergel electrolyte of the invention.

[0340] Suitable examples of the separator base used in the first type ofseparator (1) include materials commonly used as a separator base inelectrical double-layer capacitors. Illustrative examples includepolyethylene nonwoven fabric, polypropylene nonwoven fabric, polyesternonwoven fabric, polytetrafluoroethylene porous film, kraft paper, sheetlaid from a blend of rayon fibers and sisal fibers, manila hemp sheet,glass fiber sheet, cellulose-based electrolytic paper, paper made fromrayon fibers, paper made from a blend of cellulose and glass fibers, andcombinations thereof in the form of multilayer sheets.

[0341] Electrical double-layer capacitors according to the invention areassembled by stacking, fan-folding or winding an electrical double-layercapacitor assembly composed of a pair of polarizable electrodes with aseparator therebetween, each of the components being prepared asdescribed above. The capacitor assembly is formed into a coin-like orlaminate shape, then placed within a capacitor housing such as acapacitor can or a laminate pack. The assembly is then filled with thepolymer electrolyte solution of the invention, and cured by a chemicalreaction, following which the capacitor housing is mechanically sealedif it is a can or heat-sealed if it is a laminate pack.

[0342] The resulting high-performance electrical double-layer capacitorsof the invention have a high output voltage, a large output current anda broad service temperature range without compromising their outstandingcharacteristics, such as an excellent charge/discharge efficiency, ahigh energy density, a high output density and a long life.

[0343] The electrical double-layer capacitors of the invention arehighly suitable for use in a broad range of applications, includingmemory backup power supplies for electronic equipment such as personalcomputers and wireless terminals, uninterruptible power supplies forpersonal computers and other equipment, in transport devices such aselectric cars and hybrid cars, together with solar cells as energystorage systems for solar power generation, and in combination withbatteries as load-leveling power supplies.

EXAMPLE

[0344] The following synthesis examples, examples of the invention andcomparative examples are provided to illustrate the invention, and arenot intended to limit the scope thereof.

Synthesis Example 1 Synthesis of Unsaturated Polyurethane Compound

[0345] A reactor equipped with a stirrer, a thermometer and a condenserwas charged with 870 parts by weight of dehydrated ethylene oxide(EO)/propylene oxide (P0) random copolymer diol (molar ratio ofEO/PO=7/3) having a hydroxyl number of 36.1, 107.4 parts by weight of4,4′-diphenylmethane diisocyanate, and 100 parts by weight of methylethyl ketone as the solvent. These ingredients were mixed by 3 hours ofstirring at 80° C., giving a polyurethane prepolymer with isocyanate endgroups.

[0346] Next, the entire reactor was cooled to 50° C., then 0.3 part byweight of benzoquinone, 5 parts by weight of dibutyltin laurate, 16.3parts by weight of hydroxyethyl acrylate and 6.3 parts by weight of1,4-butanediol were added, and the ingredients were reacted at 50° C.for 3 hours. The methyl ethyl ketone was subsequently removed under avacuum, yielding an unsaturated polyurethane compound.

[0347] The weight-average molecular weight of the resulting unsaturatedpolyurethane compound was measured by gel permeation chromatography, andthe distributions were found to be 17,300 and 6,200.

Synthesis Example 2 Synthesis of Cellulose Derivative

[0348] Eight grams of hydroxypropyl cellulose (molar substitution, 4.65;product of Nippon Soda Co., Ltd.) was suspended in 400 mL ofacrylonitrile, following which 1 mL of 4 wt % aqueous sodium hydroxidewas added and the mixture was stirred 4 hours at 30° C.

[0349] The reaction mixture was then neutralized with acetic acid andpoured into a large amount of methanol, giving cyanoethylatedhydroxypropyl cellulose.

[0350] To remove the impurities, the cyanoethylated hydroxypropylcellulose was dissolved in acetone, following which the solution wasplaced in a dialysis membrane tube and purified by dialysis usingion-exchanged water. The cyanoethylated hydroxypropyl cellulose whichsettled out during dialysis was collected and dried.

[0351] Elemental analysis of the resulting cyanoethylated hydroxypropylcellulose indicated a nitrogen content of 7.3 wt %. Based on this value,the proportion of the hydroxyl groups on the hydroxypropyl cellulosethat were capped with cyanoethyl groups was 94%.

Synthesis Example 3 Synthesis of Glycidol Derivative

[0352] A glycidol-containing flask was charged with methylene chlorideas the solvent to a glycidol concentration of 4.2 mol/L, and thereaction temperature was set at −10° C.

[0353] Trifluoroborate diethyl etherate (BF₃. OEt₂) was added as thecatalyst (reaction initiator) to a concentration of 1.2×10⁻² mol/L, andthe reaction was carried out by stirring for 3 hours under a stream ofnitrogen. Following reaction completion, methanol was added to stop thereaction, after which the methanol and methylene chloride were removedby distillation in a vacuum.

[0354] The resulting crude polymer was dissolved in water andneutralized with sodium hydrogen carbonate, after which the solution waspassed through a column packed with an ion-exchange resin (produced byOrgano Corporation under the trade name Amberlite IRC-76). The eluatewas passed through 5C filter paper, the resulting filtrate was distilledin vacuo, and the residue from distillation was dried.

[0355] The resulting purified polyglycidol was analyzed by gelpermeation chromatography (GPC) using 0.1 M saline as the mobile phase,based upon which the polyethylene glycol equivalent weight-averagemolecular weight was found to be 6,250. Evaluation of the crystallinityby wide-angle x-ray diffraction analysis showed the polyglycidol to beamorphous. The polyglycidol was a soft, paste-like solid at roomtemperature.

[0356] Three parts by weight of the resulting polyglycidol was mixedwith 20 parts of dioxane and 14 parts of acrylonitrile. To this mixedsolution was added aqueous sodium hydroxide comprising 0.16 part ofsodium hydroxide dissolved in 1 part by weight of water, and stirringwas carried out for 10 hours at 25° C. to effect the reaction. Followingreaction completion, 20 parts of water was added to the mixture, whichwas then neutralized using an ion-exchange resin (Amberlite IRC-76,produced by Organo Corporation). The ion-exchange resin was separatedoff by filtration, after which 50 parts by weight of acetone was addedto the solution and the insolubles were filtered off. The filtrate wasvacuum concentrated, yielding crude cyanoethylated polyglycidol.

[0357] The crude cyanoethylated polyglycidol was dissolved in acetoneand the solution was filtered using 5A filter paper, then thepolyglycidol was precipitated out of solution in water and theprecipitate was collected. These two operations (dissolution in acetoneand precipitation in water) were repeated twice, following which theproduct was dried in vacuo at 50° C., giving purified cyanoethylatedpolyglycidol.

[0358] The infrared absorption spectrum of the purified cyanoethylatedpolyglycidol showed no hydroxyl group absorption, indicating that allthe hydroxyl groups had been substituted with cyanoethyl groups.Wide-angle x-ray diffraction analysis to determine the crystallinityshowed that the product was amorphous at room temperature. Thepolyglycidol was a soft, paste-like solid at room temperature.

Synthesis Example 4 Synthesis of Polyvinyl Alcohol Derivative

[0359] A reaction vessel equipped with a stirring element was chargedwith 10 parts by weight of polyvinyl alcohol (average degree ofpolymerization, 500; vinyl alcohol fraction, ≧98%) and 70 parts byweight of acetone. A solution of 1.81 parts by weight of sodiumhydroxide in 2.5 parts by weight of water was gradually added understirring, after which stirring was continued for one hour at roomtemperature.

[0360] To this solution was gradually added, over a period of 3 hours, asolution of 67 parts by weight of glycidol in 100 parts by weight ofacetone. The resulting mixture was stirred for 8 hours at 50° C. toeffect the reaction. Following reaction completion, stirring wasstopped, whereupon the polymer precipitated from the mixture. Theprecipitate was collected, dissolved in 400 parts by weight of water,and neutralized with acetic acid. The neutralized polymer was purifiedby dialysis, and the resulting solution was freeze-dried, giving 22.50parts by weight of dihydroxypropylated polyvinyl alcohol.

[0361] Three parts by weight of the resulting polyvinyl alcohol polymerwas mixed with 20 parts by weight of dioxane and 14 parts by weight ofacrylonitrile. To this mixed solution was added a solution of 0.16 partby weight of sodium hydroxide in 1 part by weight of water, and stirringwas carried out for 10 hours at 25° C.

[0362] The resulting mixture was neutralized using the ion-exchangeresin produced by Organo Corporation under the trade name AmberliteIRC-76. The ion-exchange resin was separated off by filtration, afterwhich 50 parts by weight of acetone was added to the solution and theinsolubles were filtered off. The resulting acetone solution was placedin dialysis membrane tubing and dialyzed with running water. The polymerwhich precipitated within the dialysis membrane tubing was collected andre-dissolved in acetone. The resulting solution was filtered, followingwhich the acetone was evaporated off, giving a cyanoethylated polyvinylalcohol polymer derivative.

[0363] The infrared absorption spectrum of this polymer derivativeshowed no hydroxyl group absorption, confirming that all the hydroxylgroups were capped with cyanoethyl groups (capping ratio, 100%).

Synthesis Example 5 Thermoplastic Polyurethane Resin

[0364] A reactor equipped with a stirrer, a thermometer and a condenserwas charged with 64.34 parts by weight of preheated and dehydratedpolycaprolactone diol (Praccel 220N, made by Daicel Chemical Industries,Ltd.) and 28.57 parts by weight of 4,4′-diphenylmethane diisocyanate.The reactor contents were stirred and mixed for 2 hours at 120° C. undera stream of nitrogen, following which 7.09 parts by weight of1,4-butanediol was added to the mixture and the reaction was similarlyeffected at 120° C. under a stream of nitrogen. When the reactionreached the point where the reaction product became rubbery, it wasstopped. The reaction product was then removed from the reactor andheated at 100° C. for 12 hours. Once the isocyanate peak was confirmedto have disappeared from the infrared absorption spectrum, heating wasstopped, yielding a solid polyurethane resin.

[0365] The resulting polyurethane resin had a weight-average molecularweight (Mw) of 1.71×10⁵. The polyurethane resin, when immersed for 24hours at 20° C. in an electrolyte solution prepared by dissolving 1 moleof LiPF₆ as the supporting salt in 1 liter of C₂H₅—OCO₂—C₂H₄—OCO₂—C₂H₅,had a swelling ratio of 400%.

Example 1 Polymer Gel Electrolyte (1)

[0366] An electrolyte solution was prepared by dissolving 1.43 mol/kg oflithium hexafluorophosphate (LiPF₆) in C₂H₅—OCO₂—C₂H₄—OCO₂—C₂H₅.

[0367] Next, a polymer electrolyte solution was prepared by adding thefollowing to 70 parts by weight of the above solution: 20 parts byweight of the unsaturated polyurethane compound of Synthesis Example 1,10 parts by weight of methoxypolyethylene glycol monomethacrylate(number of oxyethylene units=9), and 0.5 part by weight ofazobisisobutyronitrile.

[0368] The resulting polymer electrolyte solution was coated with adoctor blade to a film thickness of 30 μm, then heated in an incubatorat 80° C. for 1 hour to effect curing, thereby yielding a polymer gelelectrolyte.

Example 2 Polymer Gel Electrolyte (2)

[0369] A polymer electrolyte solution was prepared by the same method asin Example 1, except that a mixture of C₂H₅—OCO₂—C₂H₄—OCO₂—C₂H₅ anddiethyl carbonate in a 1:1 volumetric ratio was used instead ofC₂H₅—OCO₂—C₂H₄—OCO₂—C₂H₅ alone. The solution was similarly cured,yielding a polymer gel electrolyte.

Example 3 Polymer Gel Electrolyte (3)

[0370] A polymer electrolyte solution was prepared by the same method asin Example, except that the compound of the formula

[0371] was used instead of C₂H₅—OCO₂—C₂H₄—OCO₂—C₂H₅. The solution wassimilarly cured, yielding a polymer gel electrolyte.

Example 4 Polymer Gel Electrolyte (4)

[0372] A polymer electrolyte solution was prepared by adding and mixingthe following with 70 parts by weight of the electrolyte solutionprepared in Example 1:3 parts by weight of the cellulose derivativeprepared in Synthesis Example 2, 18 parts by weight of the unsaturatedpolyurethane compound prepared in Synthesis Example 1, 9 parts by weightof methoxypolyethylene glycol monomethacrylate (number of oxyethyleneunits=9), and 0.5 part by weight of azobisisobutyronitrile. Theresulting polymer electrolyte solution was coated with a doctor blade toa film thickness of 30 μm, then heated in an incubator at 80° C. for 1hour to effect curing, thereby yielding a polymer gel electrolyte.

Example 5 Polymer Gel Electrolyte (5)

[0373] A polymer electrolyte solution was prepared by the same method asin Example 4, except that the polyglycidol derivative prepared inSynthesis Example 3 was used instead of the cellulose derivativeprepared in Synthesis Example 2. The solution was similarly cured,yielding a polymer gel electrolyte.

Example 6 Polymer Gel Electrolyte (6)

[0374] A polymer electrolyte solution was prepared by the same method asin Example 4, except that the polyvinyl alcohol derivative prepared inSynthesis Example 4 was used instead of the cellulose derivativeprepared in Synthesis Example 2. The solution was similarly cured,yielding a polymer gel electrolyte.

Example 7 Polymer Gel Electrolyte (7)

[0375] The thermoplastic polyurethane resin solution prepared inSynthesis Example 5 was coated such as to ultimately yield a dry filmthickness of 30 μm using a doctor blade, then vacuum dried at 120° C.for 2 hours, thereby forming a polyurethane resin film.

[0376] The resulting polyurethane resin film was immersed for 24 hoursat 20° C. in an electrolyte solution prepared by dissolving 1 mole oflithium hexafluorophosphate (LiPF₆) in one liter ofC₂H₅—OCO₂—C₂H₄—OCO₂—C₂H₅, thereby preparing a polymer gel electrolyte.

Example 8 Polymer Gel Electrolyte (8)

[0377] Aside from using a 1 mol/kg solution of tetraethylammoniumtetrafluoroborate in C₂H₅—OCO₂—C₂H₄—OCO₂—C₂H₅ instead of a 1 mol/kgsolution of lithium hexafluorophosphate (LiPF₆) inC₂H₅—OCO₂—C₂H₄—OCO₂—C₂H₅, a polymer electrolyte solution was prepared inthe same manner as in Example 4. The solution was similarly cured,yielding a polymer gel electrolyte.

Comparative Example 1 Polymer Gel Electrolyte (9)

[0378] Aside from using ethylene carbonate and diethylene carbonate in a50:50 volumetric ratio instead of C₂H₅—OCO₂—C₂H₄—OCO₂—C₂H₅, a polymerelectrolyte solution was prepared in the same way as in Example 4. Thesolution was similarly cured, yielding a polymer gel electrolyte.

[0379] Each of the polymer gel electrolytes obtained in the foregoingexamples was subjected to the combustion test described below, inaddition to which its ionic conductivity was measured. The results areshown in Table 1.

Combustion Test

[0380] Pieces of manila paper measuring 1.5 cm wide, 30 cm long and 0.04mm thick intended for use as separators were immersed 5 minutes in thepolymer electrolyte solution being tested, then removed and liquiddripping from the paper was wiped off. The pieces of paper were thenheated in an incubator at 80° C. for 1 hour, yielding polymer gelelectrolyte films in which the manila paper served as the medium. Theindividual polymer gel electrolyte films were pinned on supporting wiresat 5 cm intervals and thereby horizontally secured. One end of a polymergel electrolyte film was ignited with a lighter in a draft-free state,following which the flame was allowed to self-extinguish. The burndistance (cm) and burn rate (cm/s) of the polymer gel electrolyte filmwere measured. Each of the values shown in the table below is theaverage of three measurements.

Ionic Conductivity

[0381] The polymer gel electrolyte film was placed between two coppersheets separated by a 30 μm gap and the ionic conductivities at −10° C.and 25° C. were measured by the AC impedance method. TABLE 1 Burn BurnIonic Conductivity distance rate (mS/cm) (cm) (cm/sec) −10° C. 25° C.Example 1 0.8 0.2 1.3 3.8 Example 2 2.5 0.4 1.1 3.5 Example 3 1.0 0.31.1 3.5 Example 4 0.8 0.2 1.8 4.4 Example 5 0.7 0.2 2.2 4.7 Example 60.8 0.2 2.0 4.5 Example 7 0.6 0.2 2.7 4.4 Example 8 0.6 0.2 1.2 4.2Comparative Example 1 30 0.8 0.8 3.1

Example 9 Secondary Battery Fabrication of Positive Electrode

[0382] Ninety parts by weight of LiCoO₂ as the positive electrode activematerial, 6 parts by weight of Ketjenblack as the conductive material,and a solution of 8 wt % of the thermoplastic polyurethane resin fromSynthesis Example 5 in N-methyl-2-pyrrolidone were stirred and mixed togive a paste-like positive electrode binder composition. The compositionwas coated onto aluminum foil with a doctor blade such as to ultimatelyyield a dry film thickness of 100 μm, then dried at 80° C. for 2 hoursto form a positive electrode.

Fabrication of Negative Electrode

[0383] Ninety-four parts by weight of mesocarbon microbeads (MCMB6-28,produced by Osaka Gas Chemicals Co., Ltd.) as the negative electrodeactive material and a solution of 8 wt % of the thermoplasticpolyurethane resin from Synthesis Example 5 in N-methyl-2-pyrrolidonewere stirred and mixed to give a paste-like negative electrode bindercomposition. The composition was coated onto copper foil with a doctorblade such as to ultimately yield a dry film thickness of 100 μm, thendried at 80° C. for 2 hours to form a negative electrode.

[0384] A separator base (a film having a three-layer PP/PE/PP structure)was placed between the positive and negative electrodes fabricatedabove. The resulting cell assembly was inserted in an aluminum laminateouter pack, following which the interior of the laminate pack wasevacuated so as to bring the laminate material up tight against the cellassembly. Next, the polymer electrolyte solution of Example 4 wasintroduced into the cell assembly via a needle passing through a hole inthe pack. The laminate pack was subsequently sealed and heated at 80° C.for 1 hour to effect curing via a chemical reaction, thereby giving alaminate-type secondary battery having the construction shown in FIG. 1.Included in the diagram are a positive electrode current collector 1, anegative electrode current collector 2, a positive electrode 3, anegative electrode 4, a separator 5, tabs 6, and a laminate outer pack7.

[0385] The laminate-type secondary battery produced in Example 9 wassubjected to a 50-cycle charge/discharge test in which the upper limitvoltage during charging was set at 4.2 V, the final voltage duringdischarging was set at 3 V, and the test was carried out at a constantcurrent under a current density of 0.5 mA/cm².

[0386] Following completion of the charge/discharge test, thelaminate-type secondary battery was free of any sign of electrolyteleakage or battery pack swelling due to gas evolution. Moreover, thecapacitance before and after the 50 cycles remained unchanged,indicating an absence of cycle deterioration.

Example 10 Electrical Double-Layer Capacitor (1) Fabrication ofPolarizable Electrodes

[0387] Eighty-five parts by weight of activated carbon (MSP15, producedby Kansai Netsukagaku K.K.), 10 parts by weight of acetylene black, anda solution of 8 wt % of the thermoplastic polyurethane resin fromSynthesis Example 5 in N-methyl-2-pyrrolidone were stirred and mixed togive a paste-like polarizable electrode binder composition. Thecomposition was coated onto aluminum foil with a doctor blade such as toultimately yield a dry film thickness of 200 μm, then dried at 80° C.for 2 hours to form polarizable electrodes.

[0388] A separator base (polytetrafluoroethylene) was placed between apair of the polarizable electrodes fabricated above. The resultingcapacitor assembly was inserted in an aluminum laminate outer pack,following which the interior of the laminate pack was evacuated so as tobring the laminate material up tight against the capacitor assembly.Next, the polymer electrolyte solution of Example 8 was introduced intothe capacitor assembly via a needle passing through a hole in the pack.The laminate pack was subsequently sealed and heated at 80° C. for 1hour to effect curing via a chemical reaction, thereby giving alaminate-type electrical double-layer capacitor having the constructionshown in FIG. 1.

[0389] The laminate-type electrical double-layer capacitor produced inExample 10 was subjected to a 50-cycle charge/discharge test in whichthe upper limit voltage during charging was set at 2.5 V, the finalvoltage during discharging was set at 0 V, and the test was carried outat a constant current under a current density of 1.5 mA/cm².

[0390] Following completion of the charge/discharge test, thelaminate-type electrical double-layer capacitor was free of any sign ofelectrolyte leakage or battery pack swelling due to gas evolution.Moreover, the capacitance before and after the 50 cycles remainedunchanged, indicating an absence of cycle deterioration.

Example 11 Electrical Double-Layer Capacitor (2) Fabrication ofActivated Carbon

[0391] Mesophase pitch with a Mettler softening point of 285° C.prepared by the heat treatment of residual oil from the cracking ofpetroleum was melt-blow spun using a spinneret having a row of onethousand 0.2 mm diameter holes in a 2 mm wide slit, thereby producingpitch fibers.

[0392] The spun pitch fibers were drawn by suction against the back sideof a belt made of 35 mesh stainless steel wire fabric and therebycollected on the belt. The resulting mat of pitch fibers was subjectedto infusibilizing treatment in air at an average temperature rise rateof 4° C./min, yielding infusibilized fibers. The infusibilized fiberswere then subjected to carbonization treatment in nitrogen at 700° C.,following which they were milled to an average particle size of 25 μm ina high-speed rotary mill.

[0393] Next, 2 to 4 parts by weight of potassium hydroxide was added toand uniformly mixed with 1 part by weight of the milled carbon fiber,and alkali activation was carried out at 700° C. for 2 to 4 hours in anitrogen atmosphere. The resulting reaction product was cooled to roomtemperature and placed in isopropyl alcohol, then washed with water toneutrality and dried.

[0394] The dried carbonaceous material was ground in a ball mill,thereby yielding activated carbon having a cumulative average particlesize of 2.4 μm. In the resulting activated carbon, pores having a radiusgreater than 10 Å accounted for 70% of the total pore volume and the BETspecific surface area was 90 m²/g.

Fabrication of Polarizable Electrodes

[0395] Eighty-five parts by weight of activated carbon, 10 parts byweight of acetylene black, and a solution of 8 wt % of the thermoplasticpolyurethane resin from Synthesis Example 5 in N-methyl-2-pyrrolidonewere stirred and mixed to give a paste-like polarizable electrode bindercomposition. The composition was coated onto aluminum foil with a doctorblade such as to ultimately yield a dry film thickness of 200 μm, thendried at 80° C. for 2 hours to form polarizable electrodes.

[0396] A separator base (polytetrafluoroethylene) was placed between apair of the polarizable electrodes fabricated above. The resultingcapacitor assembly was inserted in an aluminum laminate outer pack,following which the interior of the laminate pack was evacuated so as tobring the laminate material up tight against the capacitor assembly.Next, the polymer electrolyte solution of Example 8 was introduced intothe capacitor assembly via a needle passing through a hole in the pack.The laminate pack was subsequently sealed and heated at 80° C. for 1hour to effect curing via a chemical reaction, thereby giving alaminate-type electrical double-layer capacitor having the constructionshown in FIG. 1.

[0397] The laminate-type electrical double-layer capacitor produced inExample 11 was subjected to a 50-cycle charge/discharge test in whichthe upper limit voltage during charging was set at 2.5 V, the finalvoltage during discharging was set at 0 V, and the test was carried outat a constant current under a current density of 1.5 mA/cm².

[0398] Following completion of the charge/discharge test, thelaminate-type electrical double-layer capacitor was free of any sign ofelectrolyte leakage or battery pack swelling due to gas evolution.Moreover, the capacitance before and after the 50 cycles remainedunchanged, indicating an absence of cycle deterioration.

[0399] The foregoing results show that the polymer gel electrolytes ofthe invention have a good thin-film strength and good temperatureproperties, and also have a high ionic conductivity. With thiscombination of desirable qualities, the polymer gel electrolyte wasfound to exhibit excellent characteristics when used in secondarybatteries and electrical double-layer capacitors.

[0400] Therefore, as described above and demonstrated in the foregoingexamples, the invention provides secondary batteries which can operateat a high capacitance and a high current, which have a broad servicetemperature range and a high level of safety, and which are thusparticularly well-suited for use in such applications as lithiumsecondary cells and lithium ion secondary cells.

[0401] The invention also provides electrical double-layer capacitorswhich have a high output voltage, a large output current, a broadservice temperature range, and excellent safety.

[0402] Japanese Patent Application No. 2000-371277 is incorporatedherein by reference.

[0403] Although some preferred embodiments have been described, manymodifications and variations may be made thereto in light of the aboveteachings. It is therefore to be understood that the invention may bepracticed otherwise than as specifically described without departingfrom the scope of the appended claims.

1. A polymer gel electrolyte comprising: an electrolyte solutioncontaining a plasticizer with at least two carbonate structures on themolecule and an electrolyte salt, and a matrix polymer.
 2. The polymergel electrolyte of claim 1 which consists essentially of the plasticizerwith at least two carbonate structures on the molecule, the electrolytesalt, and the matrix polymer.
 3. The polymer gel electrolyte of claim 1or 2 in which the plasticizer with at least two carbonate structures onthe molecule is a compound of general formula (1) below

wherein R¹ and R² are each independently a substituted or unsubstitutedmonovalent hydrocarbon group of 1 to 10 carbons, and R³ and R⁴ are eachindependently a substituted or unsubstituted divalent hydrocarbon groupof 1 to 20 carbons, with the proviso that any two of the moieties R¹,R², R³ and R⁴ may together form a ring; X is —OCO—, —COO—, —OCOO—,—CONR⁵—, —NR⁶CO—(R⁵ and R⁶ being hydrogen or an alkyl of 1 to 4carbons), —O—or an arylene group; and the letters m, n, k and p are eachindependently 0 or an integer from 1 to
 10. 4. The polymer gelelectrolyte of claim 3, wherein some or all of the hydrogen atoms on theplasticizer of general formula (1) having at least two carbonatestructures on the molecule are substituted with halogen atoms.
 5. Thepolymer gel electrolyte of any one of claims 1 to 4, wherein the matrixpolymer is an unsaturated polyurethane compound prepared by reacting:(A) an unsaturated alcohol having at least one (meth)acryloyl group anda hydroxyl group on the molecule; (B) a polyol compound of generalformula (2) below HO—[(R⁷)_(h)—(Y)_(i)—(R⁸)_(j)]_(q)—OH  (2) wherein R⁷and R⁸ are each independently a divalent hydrocarbon group of 1 to 10carbons which may contain an amino, nitro, carbonyl or ether group, Y is—COO—, —OCOO—, —NR⁹CO— (R⁹ being hydrogen or an alkyl group of 1 to 4carbons), —O— or an arylene group, the letters h, i and j are eachindependently 0 or an integer from 1 to 10, and the letter q is a numberwhich is ≧1; (C) a polyisocyanate compound; and (D) an optional chainextender.
 6. The polymer gel electrolyte of any one of claims 1 to 4,wherein the matrix polymer is a polymeric material having aninterpenetrating network structure or a semi-interpenetrating networkstructure.
 7. The polymer gel electrolyte of claim 6, wherein thepolymeric material having an interpenetrating network structure or asemi-interpenetrating network structure comprises a hydroxyalkylpolysaccharide derivative, a polyvinyl alcohol derivative or apolyglycidol derivative in combination with a crosslinkable functionalgroup-bearing compound, part or all of which compound is the unsaturatedpolyurethane compound of claim
 5. 8. The polymer gel electrolyte of anyone of claims 1 to 4, wherein the matrix polymer is a thermoplasticresin containing units of general formula (3) below

in which the letter r is an integer from 3 to 5, and the letter s is aninteger ≧5.
 9. The polymer gel electrolyte of any one of claims 1 to 4,wherein the matrix polymer is a fluoropolymer material.
 10. The polymergel electrolyte of any one of claims 1 to 9, wherein the electrolytesalt is at least one selected from the group consisting of alkali metalsalts, quaternary ammonium salts, quaternary phosphonium salts andtransition metal salts.
 11. A secondary cell comprising a positiveelectrode, a negative electrode and an electrolyte, wherein theelectrolyte is a polymer gel electrolyte according to any one of claims1 to
 10. 12. The secondary cell of claim 11, wherein the negativeelectrode includes a negative electrode active material which islithium, a lithium alloy or a carbon material capable of adsorbing andreleasing lithium ions.
 13. The secondary cell of claim 11 or 12,wherein the positive electrode includes a positive electrode activematerial which is an electrically conductive polymer, a metal oxide, ametal sulfide or a carbonaceous material.
 14. An electrical double-layercapacitor comprising a pair of polarizable electrodes and an electrolytebetween the polarizable electrodes, wherein the electrolyte is a polymergel electrolyte according to any one of claims 1 to
 10. 15. Theelectrical double-layer capacitor of claim 14, wherein the polarizableelectrodes contain activated carbon which is prepared by subjecting amesophase pitch-based carbon material, a polyacrylonitrile-based carbonmaterial, a gas phase-grown carbon material, a rayon-based carbonmaterial or a pitch-based carbon material to alkali activation with analkali metal compound, then grinding the activated carbon material.